Here's how to replace a clock spring on a Toyota or Lexus vehicle.
This video also goes into the tear-down of how a clock spring works.

A clock spring is responsible for translating the electronic inputs from your rotating steering wheel (such as steering wheel audio controls, horn, airbag, cruise control, etc.) into the car.

A clock spring consists of a long ribbon cable wrapped up in a spiral. Its length allows it to rotate roughly 5 turns before the wire comes under tension. The housing is simply made of plastic with sturdy connections at either end for the airbag and accessories.

Often an airbag light on the dash, or lack of steering wheel controls (horns, audio control, etc) can be traced to a bad clock spring. Usually the thin ribbon cable is severed at some point and needs to be replaced or patched.

The clock spring is located behind the steering wheel. Be cautious when working around the airbag as its an explosive. Disconnect the battery and let the system drain for 15 mins before removing the airbag.

Also be sure to mark your steering wheel position before removing it from the splines. That way it can be reinstalled in the exact straight position.