1996 Toyota 4Runner 4WD model shifter

I just purchased a used 1996 Toyota 4Runner Limited Edition 4WD automatic. I know how to use the normal automatic shifter, but can anyone explain to me what is the samll shifter next to it do and when should I use it. It has a 4WD button, I use it to turn 4WD off and on.

It is my first 4WD truck. Thanks for you time.

Look on the driver's-side front visor. There should be a vehicle-specific instructions card that explains when and how to use your 4WD capabilities.