If you cannot move the shifter out of the park position then you have a problem with the shifter cable or the brake safety lock. If you can move the shifter to the drive position, and it doesnt go in gear then you are a few quarts low on transmission fluid
You may want to look at your fuse panel. Possibly the brake,
If by some chance you are asking " why is my shifter stuck in park and you cannot shift out of park " then just turn the key to the first notch, no ign. lights, then put the shifter in neutral, start the car and drive to your local garage. They can fix it for you.
Insert key. Turn to ACC. Push brake. Push button on shifter. Move shifter out of park. It helps if park lock cable is not broken, and if vehicle is not on an incline.
overdrive off, on a 2003 it is in the end of the gear select lever If it's the hidden button I think you are referring to, should you experience electric release failure (where you cannot get the shifter out of park) pushing this button is a manual over ride allowing you to get the shifter out of park
Wiggle the steering wheel back and forth and run the transmission shifter down then put it firmly back into park.
transmission shift bolt loose try pushing gear shifter all the way back to park
Try putting the shifter in neutral and try it. If not pull the shifter in to park, but pull it into park and turn key.
Make sure the shifter is all the way in park, if it is not in park, the key will not come out. You might want to wiggle the shifter to make sure it is all the way in park.
Ford Explorer Column Shifter Lever Bracket Repair
There is a plastic rod inside of the shifter arm, it unlocks the shifter from the park position when the button on the shifter handle is pressed. So, press in on the shifter button and pull the shift handle straight UP (you might have to pull hard). You should be able to remove the broken pieces of the plastic rod with some wire. You might have to go to a junk yard for a replacement.
The shifter is held in park unless you depress the break look their for the lock out controllers