Bowmode controls how you will fire arrows and bolts.

The options are:

Normal: As you would expect.

Threewide: Fires three arrows in parallel.

Spreadshot: Fires three arrows which spread out over distance.

Fire<direction>:  Locks in the direction the missiles will fire, 
specify by compas position: 
firenorth, firene, fireeast, firese, firesouth, firesw, firewest, firenw

Bestarrow: Selects and fires the probable best arrow for from your inventory.