The doctor thinks i broke my left talus bone. what does the talus bone do?

Part of Ankle Joint: The talus bone or astragalus bone is the bone immediately below the leg bones. So it is the bottom part of the ankle joint. It can be injured during an ankle sprain where part of the tailar dome is injuried. The cartiledge can crack or have a defect sometimes this is missed on a plain x-ray film. This is one case where an MRI study is very important to help diagnose this type of cartiledge injury.

Foot bone: The talus is a foot bone that makes up one of three bones in the ankle joint, along with the tibia and fibula. Severe fractures of this bone are serious and can comprise the ankle joint.