Once your Blood Elf reaches level 20, you can learn the journeyman riding skill and get your Hawkstrider mount right outside of Silvermoon City. After exiting Silvermoon City through the south exit, head east down the road until you see a building on the left side. It will say Thuron's Livery on your map. Inside the building you can learn the riding skill, and the vendor outside the building will sell you a mount. While you can get riding training from any riding trainer, your land mounts can only be purchased from Thuron's Livery until you reach exalted reputation status with another Horde city faction.