What does it mean when one of your ankles is constantly cracking when you walk? how can you fix it?

Couple of things: Sometimes it can be your peroneal tendons (those that run along the outside of your ankle) rubbing against the fibular bone or the soft tissue structure that hold them in place. Sometimes, it is merely air escaping from the joint capsule. If it is not painful, i don't think you have to worry about it though.

This is normal: Usually when one of your ankles is cracking and there is no pain, it is the tendon that comes around the ankle the will slip in and out of the ankle groove that is made for it. This will create the cracking sound. It is nothing to worry about, but if you have to have the sound go away, then see your podiatrist who will do a surgery to deepen the groove and avoid the tendons from popping out.