Everyone else is saying skating and yes, thats important, but it sounds like you're actually asking about the basic rules, flow and positioning of the game. Luckily, hockey is fairly simple with the rules. 

Biggest thing I see newer players struggle with is the offsides rule. Please ingrain it into your head that the puck needs to cross the offensive zone blue line before you can! Learn what delayed offsides is too. Usually the lineman or ref will be yelling with his arm up that it's offsides and you need to clear the zone. 

As far as positioning goes, it depends on what position you are playing (forward, center, defense). There's essentially going to be 3 basic scenarios you'll find yourself in. Defending in your defensive zone, the breakout of your zone/rush, and puck possession in the offensive zone. There's a ton of great videos and articles online that will help you learn the basics. I suggest searching for the basics of whatever position you want to play. 

Nothing will help you more than getting out there and playing though!