As a level 20 draenei paladin on a trial account in World of Warcraft how do you get a mount

For a Draenei, head to the Exodar, your races capital city. There you can talk to the riding trainer that is just outside the entrance to the Exodar. The NPC you are looking for is called Aalun.

It should cost around 4g (less if you have a lot of reputation).