Venture to Alterac Valley, located in the Alterac Mountains. Find and speak with Warmaster Laggrond - who stands outside the tunnel entrance - to begin your career as a soldier of Frostwolf. You will find Alterac Valley north of Tarren Mill at the base of the Alterac Mountains.
The drums of war sound off in a distant land, [class]. The favored clan of your Warchief is under attack from the nefarious Stormpike Guard of Ironforge.
By the looks of you, I can discern that you are indeed battle hardy and prepared to take on the cause of the Frostwolf.
It is you who must now take the next step in your evolution.
North of Tarren Mill, in Alterac, you will find the entrance to Alterac Valley. It is there that you will find Warmaster Laggrond. Hurry [class], for the battle is upon us!