"The Felsteed is the 'free mount' that Warlocks receive at level 40. Other than Paladins, all other classes must pay 10Gold for a mount and 90Gold for training to ride it (these prices can be lowered by being Honored with the mount's city (and pre 2.0 by obtaining the Sergeant rank)). This is a great help since Warlocks must purchase spells for their summoned minions as well. You also gain riding skill 75."
You learn to summon your mount AND the riding skill to use it. Just wanted to clear that up for those who were wondering, after changes were made to the riding skill mechanics a while back (including myself).