Is the winger supposed to stay wide? Does he have a special function apart from piercing through the wing? Does he have to track back?
In the modern game there are two kind of wingers: wing-backs and attacking wingers
The difference between a wing-back and a full-back is that the former has more attacking duties, mostly because there are no wide midfielders or wide attackers in the team. Usually a 5-defenders formation contains wing-backs, where you have 3 center backs, so the two side defenders can roam almost freely on the wings and help the attack. Having 3 central defenders protects the defence on counters in the absence of the side defenders. 4-men-defences can also have wing-backs: just look at Marcelo (Real Madrid) or Dani Alves (Barcelona), they help a lot in the attack and usually are part of the attacking construction. But in their cases the team needs to be able to cover their defensive spots. Usually a midfielder can conver in case of a counter. The wing-back's job in attack is to make runs, receive the ball wide of the pitch, cut it back or cross it to the froward(s).
An attacking winger (or wide forward) is an offensive player who usually receives the ball close to the side line, dribbels, cuts inside or crosses the ball. They are usually very fast and have great ball skills. Usually they play in a 4-3-3 or 4-2-3-1 formation in attack, but often the formation changes to 4-5-1 or 4-4-2 when defending and the wingers become right and/or left defensive midfielders. Example: Gareth Bale (Real Madrid) is the right forward on attack and becomes the right midfielder on defense.
While wingers mostly play close to the side line, it's not usual for them to cut into the middle, especially in attack. Wide forwards often cut inside to shoot with their inside foot, like Arjen Robben (Bayern), or to stretch the defense.
In soccer (football), a winger is an attacking midfielder in a wide position. Wingers are usually players of great pace or dribbling ability so as to provide cut-backs or crosses from which strikers can score. Their main function is to support attack from the wings. Wingers do lots of high-speed running from defence to attack.