How do I get new warlock summons?

First time WoW player here. Can't find any guides on WotLK warlock demons, can someone please point me in the right direction?

You only get the Imp as a skill at the trainer, and you can learn the Felguard with the appropriate Demonology talent. The others are learned as rewards from Warlock specific quests. After a quick search I found this, seems to talk you through those along other things, give it a look.

http://forum.warmane.com/showthread.php?t=67185

Basically all the warlock trainers will (should, hey it's Warmane) give you the initial quest whenever you reach the appropriate level for a new minion.
Pack a big lunch, because getting them involves a lot of travelling.