Bring 5 Singed Scales to Uzzek at Far Watch Post in the Barrens.
As a warrior, one of our most crucial tasks is... protection. We are the shield of the Horde, and we keep our weaker brethren safe. If you are to join in our ranks, then you must prove your mettle to me.
Go to Thunder Ridge in Durotar, where live the lightning hides and thunder lizards. Hunt the beasts! Show me you are tougher than they! Brave their assaults and bring me a stack of their singed scales as proof.
Do this, and then I will teach you.