Inside the cab, far on the passenger side, there's a door in the front panel. Open that door. Inside you should find a book, titled 'Operators Manual' or something similar. Open that. Somewhere on the first few pages you will find what is called a table of contents. There will be an entire section of that magnificent book dedicated solely to teaching you how to shift your rig from 2WD to 4, and back again. If you have difficulty reading it, step away from the truck, call a towing company, and have it delivered to the nearest Chevy or Ford dealer, and trade that thing on a POS Colorado or Ranger.
I'm not poking fun at you or making light of your situation, unless of course you are a big dummy. You bought a Tacoma, so you ain't stupid. Maybe just a little too excited to think straight.