CM is easily the single weakest hero in the game right now, don't expect to do anything but die with her.
In fact, be fully prepared to be as good as 0-8 in DotA if you play pure supports. No one can protect you from death like they can in LoL - the support will die just to residual AoE if he doesn't position properly, and if he DOES position properly, most carries can still kill you in two hits late game. Your job is really to prop up the carry early game and to go into team fights late game as a sacrifice so the carry has two more seconds to do his job, or maybe one fewer stun to deal with.
Teleporting is a huge deal in DotA, the higher up in skill you get the more you should expect every fight near a tower to end with 2-3 enemies teleporting in to kill you. That's what towers are for In DotA; in LoL they protect you with absurd amounts of damage, in DotA they're walls against pushing and teleport spots.
Abilities you just have to study the learn tab until you know what everyone does, honestly, same as you would for any other game =p