First aid for ankle sprain is:

R - REST the affected area.
I - IMMOBILIZE the area and limit the use of the ankle.
C - COMPRESSION (apply cold compress/packs to the painful area).
E - ELEVATE the lower leg to minimize swelling.

This is performed 3-5 times daily for 1- 2 weeks. If symptoms persist, see your doctor.

Brace and rehab. Crutches for a short while

Most ankle sprains do not require surgery. If I were seeing this patient I would start him on anti-inflammatories and I would send him to physical therapy. Sometimes bracing can help as well.

Ankle sprains do really well without surgery, regardless of severity. Make sure no fractures (x-rays). Ice, ankle exercises, and often people like to use 'lace-up ankle braces.'

Rest, ice 20 minutes every 2-3 hours, elevate on 2-3 pillows to keep above chest level, mild compression with ace wrap, alternate acetaminophen and ibuprofen as guided by weight/instructions on bottle, as needed for pain/swelling - provided you have no allergies to them.

Treat symptomatically. 1st ICE to reduce the swelling. Ultimately with heat. Wrap as required. OTC analgesics.

It honestly depends on how badly sprained it really is. In most cases, though, it'll be fine with a boot and rest from activity while going through several weeks of rehab. Ankle sprains rarely need surgery.

Rest
Ice
Compression
Elevation