For questions generally relating to the competitions and individual events falling into the family of "track and field" sports, i.e. foot races including hurdles (but excluding marathons and long-distance running; see the "marathon" tag), jumping, vaulting, javelin, shot put, hammer throw, etc.
Track and field is a family of competitive events, including foot races, jumping competitions, and throwing/hurling competitions. It is among the oldest forms of formal athletic competition, dating back to ancient Greek and Roman eras, including the ancient Greek Olympic Games.
Modern track and field events include:
Running races: 50m, 100m, 200m, 400m, 800m and 1600m (~ 1 mile) distances are common for individual events. Competitors run on an oval track, in individual lanes (with starting positions staggered on events that require running around the circular ends of the track to provide the same overall distance for all runners). Contestants line up on starting blocks, set, and await a starting gun to begin the race. The first runner to cross the finish line, without leaving their lane or committing some other fault such as a false start, wins the race.
Modern races are typically run in heats, allowing for more competitors than there are running lanes on the track; runners compete either to win the heat, or to have one of the best times among all runners in a set of heats, each of which earns them a spot in the next higher stage of the event.
Hurdling: Usually seen in 100m and 400m lengths, hurdling is similar to a normal running race, but evenly spaced in each runner's lane are 10 gates or "hurdles" which they must jump over while running. Several hurdle heights are common, depending on age and gender of the runners. When hurdling, it is acceptable to knock the hurdle over (which they are designed for), but all ten hurdles must be cleared by passing over them in some form (and it is preferred to clear the hurdle cleanly as hitting the hurdle causes the runner to lose speed) Again, hurdle races are commonly run as heats allowing more competitors to race than the track has lanes by advancing the runners with the fastest times at each level to a higher stage of the event.
Relay racing: Similar to a running race, a relay race is a team event in which four runners on a team take turns running "legs" of the race. The first runner starts off a block, similar to a running race. They run their allotted distance (1/4 of the total distance) carrying a short wooden pole or aluminum tube called a "baton". At the end of their leg, the next teammate awaits them, and the runner must pass the baton to their teammate in front of a line on the track (the teammate is allowed to build a running start but may not cross the exchange line without the baton). This happens two more times before the final runner for each team carries the baton across the finish line. Relay races are commonly seen in 400m and 1600m total distances, with each runner running 1/4 of that distance; the events are usually notated as 4x100m and 4x400m. Other lengths, such as 4x200m, 4x800m and 4x1600m are sometimes seen. Also seen is the Medley Relay, a relay race in which each leg is progressively longer; the two most common medleys are 1200-400-800-1600 (a Distance Medley; total distance 4000m) and 400-200-200-800 (a Sprint Medley, total distance 1600m).
Long Jumping: Competitors start at the end of a running track, at the end of which is a long sand pit. The competitor runs along the track to a line at the end, at which they jump out across the sand pit, the objective being to cover the most distance, as measured by the first disturbance made in the sand by the competitor's body, hands, feet or clothing. Each competitor typically gets three attempts and their best distance counts. There is also a standing long jump variation, where the competitor does not get a running start but simply stands at the jump line and makes their leap.
Triple Jumping: Similar to long jumping, but at a point further back in the running lane, the competitor must begin the first of three leaps; typically first with one foot, then with the other, and finally with both out into the sand pit. The total distance of all three jumps is measured. There is a standing triple jump variant.
High Jumping: Competitors approach a bar set at a given distance above the ground, with any starting height offered by the judge and accepted by the competitor. They must, without assistance from any device, propel their body over the bar without knocking the bar off of the pegs holding it up. Each competitor gets three tries at a given height, and as soon as they clear it they may proceed to the next higher distance, or if they fail to clear it in 3 tries they are eliminated. The jumper who clears the bar successfully at the highest distance wins; if there is a tie for height, the jumper who cleared that distance with fewer failed attempts win. If it's still a tie, a "jump-off" is held; the jumpers each get one attempt at the next higher distance, and the bar is raised if both clear it and lowered if both fail, until only one jumper clears the bar on their attempt. There is a standing high jump variant where no moving start is allowed.
Pole Vaulting: Competitors carry a long flexible pole which they hold at one end as they run down a lane. At the other end of the lane is a bar placed on pegs, and a small hole or trench in the ground. The vaulter must put the other end of the pole in the hole or trench; the pole will then bend, storing the vaulter's forward motion, and straighten, propelling the vaulter upwards. Then, similar to high jumping, the vaulter must pass their entire body over the bar without knocking it off the pegs. Again similar to high jumping, each vaulter gets three attempts at a given height, and the vaulter who clears the greatest height wins with ties broken first by the number of failed attempts and then by a "vault-off".
Discus Throw: The discus is a lens-shaped disc of wood, metal, ceramic and/or synthetic, weighing 2 kilograms for men and 1 kilogram for women and juniors. The thrower starts in a circle 2.5m in diameter, and attempts to propel the discus through the air into the "fair zone" (described by an angle of 35* drawn on the field with its vertex at the thrower's feet), covering the greatest distance possible. The thrower may not leave the throwing circle, but there are no other major rules concerning form or method of throwing.
Shot Put: The "shot" is a metal or synthetic sphere 5.75kg in weight (for Olympic men's events; 16lb for NCAA men's events) resembling a cannonball. Competitors stand in a circle 7 feet in diameter with a "stop board" 10cm high at the front of the circle. They heft this shot to their neck with one hand, and then with a pushing motion attempt to heave it as far as possible; the distance is measured from the outer circle to the first mark made in the ground by the shot. There are specific technique guidelines which must be followed when shot putting.
Hammer Throw: The hammer is a metal sphere 16 pounds in weight (for men's events) to which is attached a wire or pole 3 feet, 11 inches long with a handle at the end. Throwers stand in the same circle as for a discus throw, swing the hammer up into the air and then around their body one to four times before releasing it; the object, as with other throws, being the longest distance from the edge of the circle to the first point of impact of any part of the hammer. In the original form of the competition still practiced in Scotland, an actual sledge hammer is thrown (hence the name), but for most competitions including collegiate and Olympic events, a ball with a wire or chain and handle is used.
Javelin Throw: The javelin is a pointed throwing spear 2.6m long and weighing 800 grams (for men's competitions). Competitors run down a short lane carrying the javelin, and then heave it into the air, going for the best distance. The javelin must stick into the ground at its initial point of impact, and must be within the "fair zone' (an angle similar to the discus but only 28 degrees) for the throw to count.
Decathlon: The decathlon is a sequence of ten track and field events, a combination of running, jumping and throwing, in which each athlete competes in each event and the winner is the best overall performer, as scored using metrics based on the competitor's distance, height or time in each event as applicable. The ten events are 100m, 400m and 1500m running races, 110m hurdles, long jump, high jump, pole vault, discus, hammer throw and javelin.
Heptathlon: Similar to the decathlon but intended for female competitors, the heptathlon is seven events: 200m and 800m running races, 100m hurdles, long jump, high jump, shot put and javelin. Competitors are scored on their performance in each event using a mathematical metric, and the highest overall score wins.
Women's Pentathlon: Not to be confused with the Olympic Modern Pentathlon (an event combining fencing, horse racing, running, shooting and swimming), the women's pentathlon is the 800m running race, 100m hurdles, long jump, high jump and shot put. It has been replaced in the Olympics with the heptathlon as of 1984, but is still seen in junior athletic events.
Marathon: Usually its own event, the marathon is one of the original events of the modern Olympics, and is modeled after Pheidippides' victory run from the site of the Battle of Marathon to Athens to bring news of the Greek victory. The modern marathon is 26.2 miles (42.195 km) and is the longest Olympic running race distance, with the event at the Olympics usually ending at the track-and-field stadium with one lap around the track.
Half-Marathon A long-distance running race exactly half the distance of a marathon, 13.1 miles, typically offered to runners at events that also include a full marathon. It is not an Olympic event, however the 20km race walk is a similar distance (though the competitors are required to "walk" - to have one foot in contact with the ground at all times - and so the pace is typically slower than cross-country running).