Nothing. Bone will heal at its own rate. Treatment involves aligning the broken ends so they heal straight. It can be done externally with a cast or fixator, or internally with surgical placement of pins, plates and rods. Which is done depends on many factors.
See Orthopedist. Most broken bones need immobilization, which often means a cast. See the specialist.
See below. Usually relative rest is all you need to employ to get adequate healing. Rarely, they need to be removed surgically if there is chronic pain.