I found some information on rules, but I never found a clear answer to what should be done when a served ball touches the net.
Is it point for opponent, or should the serve be redone?
If redone - will it be redone regardless of how many times it hit the net?
If the serve touches the net, it is a let, and you must serve again. If it touches the net and lands on the floor, you lose a point. If the serve goes into the net, you lose the point.
According to the USATT Rules
2.9 A Let
2.9.1 The rally shall be a let
188.8.131.52 if in service the ball, in passing over or around the net assembly, touches it, provided the service is otherwise good or the ball is obstructed by the receiver or his/her partner;
Which means you must serve again if other than touching the net the service would be good. other wise rule 184.108.40.206 would apply:
2.10 A Point
2.10.1 Unless the rally is a let, a player shall score a point
220.127.116.11 if the opponent fails to make a correct service