What is this?

Hey all-

I have a 1999 Toyota Camry LE that a neighbor basically gave to me, such was the bargain. I don't have a manual for it, however, and don't know what a certain button is. Below is a picture. The button is over the "P" symbol on the shifter console and appears to be missing a cover. Can anyone tell me what it is, how to use it, etc?

that bottom overrides the shift lever when its in park with out the key in the ignition cylinder.