The driver side door of my 2006 Thunderbird won't open from the inside. It opens just fine from the outside. How can I fix this?

Spray it with lube or cleaning solvent, if that doesn't help you'll have to pull the inside door panel and make sure all the locking rods are connected, at least the one from the inner door handle to the locking mechanism. The plastic clips that hold them in place can break.

If the inside door handle goes through the motions of opening the door but doesn't, then remove the door panel and you should be able to see what has come loose. The repair could be as easy as inserting the rod in the hole and a cotter pin.