As a tank how do you keep enemies from attacking your teammates?

the title sums it up

For Protection Warrior, two of the skills that pull mobs off teammates are:

Taunt is your single-target taunt ability. Casting Taunt significantly increases your threat generation for its duration. If you are having trouble building threat, deal as much damage as possible in this window.

Heroic Throw deals little damage, but generates a decent amount of threat. It has no cost and no cooldown. Use it to gain aggro on distant enemies. Also, if you are ever out of range of an enemy and cannot get back into melee range for whatever reason, you can spam Heroic Throw for a tiny bit of extra damage.

See the icy veins class guides for rotations, talents, priorities etc. the more damage you do the more aggro you generate as well