I am new to the game and started a tank thinking it would be similar to other MMO's I played....I was wrong.

I am learning slowly the Gladiator/Pali role.

I seem to have issues with multiple mobs and holding agro. I got yelled by a player, he told me not to sleep targets? What does sleep mean?

Any tanking advise would be greatly appreciated. Sorry if this post is in the wrong location and thanks in advance.