What to do for a broken collarbone?

Varies. Many clavicle fractures do very well with short term immobilization with a sling or figure of 8 harness, a small percent require surgery. I would discuss the specifics of your case with an orthopedic surgeon.
Collarbone. Depends on extent of clavicle fracture, if displaced, discomfort and how long ago it occurred. If not complicated, traction helps ease pain until heals. Consult your doctor for x-ray and tx recommendations.
Clavicle Fracture. For "broken collarbone"/clavicle fractures that are nondisplaced or minimally displaced, treatment consists of a sling, pain medication, and regular elbow range of motion exercises (to prevent frozen shoulder). Emergent orthopedic referral is required for open fractures (if the broken bone sticks out through the skin) or f the bone pushes the skin up "like a tent". Plain xrays make the diagnosis.
Depends. It depends on where the collarbone is broken and whether the bone fragments are displaced or not (lined up or not). Treatment ranges from a simple sling to needing an orthopedic consult for advanced treatment.