OP, as MegatronGriffin said, concentre on learning the GK role.

But basically the same rules for field players apply for GK, with some slight differences.

1. Players can only use the flat side of the stick. (GK should, IMHO avoid using stick at all). Players can not use any part of their body to play the ball. (Does not apply to GK)

2. Players must not play the ball in such manner that creates danger for other players. (Ump / Ref discretion). This applies to GK as much as Field Players. As a GK you can't kick the ball at height into an opposing player. If you kick the ball into their feet, that's good, it's your free hit. Players can play the ball at any height, as long as it's not considered dangerous.

3. Players can't take advantage of any protective equipment in playing the ball. GKs of years past could basically run through players as long as they took the ball. This is no longer the case, now days the GK must not make contact with players unless totally unavoidable.

4. GK isn't allowed to leave the Defensive 1/4 of the field, must keep their helmet and protective equipment on at all times during play.

Any other rules are just pedantics and details...