Go to your race's main city (Silvermoon) and you can look for the mount trainer. To ride the mounts of other races, you have to be exalted with them first. For example, to ride wolves, have to be exalted with Ogrimmar I believe. Easiest way is to reach lvl 51+, play AV, AB and WSG 30 times each (total of 90 times) or till you accumulate 30 medals from each of these BG, and at level 60, learn epic mount riding and buy the AV wolf mount.