what is 4WD

Welcome to the group. There are a few trolls here, but they arn't difficult to spot.

Part Time is for use only in off-road (gravel, loose dirt, rocks) use it on dry pavement and you risk grenading your transfer case. As you said, the front and rear driveshafts are essentially locked. Because the front and rear tires are not identical, one will build up tension and eventually you will get a chirp as the axle unloads. Too many of that and wave bye bye to your transfer case or any weak part of the drive system.

Part time on ice can cause you to swap ends, so get used to how your vehicle handles. I always suggest a nice open empty parking lot.

Full Time is as it says, Full Time. You can use it anywhere at any time. I have a ZJ with the Quadratrack Full Time case. So basically that's my only choice. It's Part Time because there is a limited slip clutch/viscous coupling that keeps it from binding up.

The most important thing to know about 4wd is you may be able to go further or faster in bad conditions but you will stop the same way every other vehicle does. So don't over estimate your abilities.

Or as one old timer put it. 4WD lets you get into even worse sitiuations than 2WD. :)

A site/board to read.