This NPC gives a brief introduction to new players on how the battle of Alterac Valley works. He's found at the very beginning of the tunnel which leads out to the battlefield.

Should bring you through the basics if you don't already know, like what Alterac Valey is such as both factions' captains, leaders, and bases. He'll also inform you on how graveyards, mines and towers work.

More basic reading can be found on Blizzard's Alterac Valley General Information.