my driver side door wont lock with either fob or key on my 2001 explorer

There could be a couple of problems. corrosion and crud has built up inside the door. You probably cannot generate enough torque with the key to overcome the resistance. Remove the door and try to move the button into the up position by grasping the rod and lifting. If you cannot, the lock mechanism is shot and will require replacing.

what do you mean by lock mechanism?

Remove the inside door panel, leave the window up. you will see a rod extending up from lock mechanish to the button which you can see. Grasp the rod and lift up. If it does not lift up the mechanism will require replacement or oiling. You probably cannot see the nechanism as it may be behind steel bracing on the inside of the door. If you look at the edge of the door you can see the locking mechanism which engages the post screwed into the door jamb when the door is closed. There may be three screws holding it in which are visible. It is not each to get out as small hands are usually a plus in this situation. There is also an electrical connection which controls the lock/unlock function of the key fob/switch on the door. If you have never doon this before I recommend you leave it to someone who has. Basically, you have to be able to view the setup with your mind's eye and see with the tips of your finger.

Mine was rusted pulled it out shot it with wd40 let it sit for awhile then lightly tapped on the the lockmechanism till it moved tapped it back to unlock by then I was able to move it by hand so I moved it back and forth a couple times till I lt felt pretty loose then sprayed silicone grease on it and moved it a couple times sprayed some more moved it a couple times and it works fine now. I couldn't push the lock down or get it to lock with the key. But now I can do both.