Explain to me how rear differential works on my 1999 Ford Ranger 4x4?

So i had it in standard 2wd and was pulling into the driveway just using idle and not actually accelerating and my left rear tire came on an ice patch and started spinning kinda fast. I accelerated and just the left wheel was spinning but i wasn't moving. I had to put it in 4wd in order to move forward. So my question is if i was in 2wd and it is a rear wheel drive truck than why wasn't the right rear wheel moving at all?

I know this has something to do with types of differentials but i'm ignorant about this stuff.

I thought both rear tires where pushing the truck when it is in 2wd.

Also, if i put it in 4x4 does that mean that all 4 tires are pushing the truck?

If someone can explain how all this works in very layman's terms i would appreciate it.

What you saw is the difference between an open diff and a locked or limited slip diff. An open diff does have a "power wheel" and typically it is the one on the passenger side of the vehicle.

A limited slip diff acts a bit differently where it does put power to both wheels but can also slip so one wheel can move slower than the other.

A fully locked diff (sometimes accomplished by welding the spider gears of an open diff, not recommended) operates both wheel at the same speed and power no matter what. The problem with a locked diff is that when a car turns a corner the inner wheel turns less than the outer wheel, so if the wheels want to spin the exact same, but the car is turning corner the difference is made up by the outer wheel stopping and sliding in the turn.

Some trucks (such as TRD model tacomas) come with an optional locking diff which can be activated by a switch in the cab.

Your truck likely only uses 2 tires as power tires when you are in 4wd. Usually the passenger rear and the drivers front. Te front diff is the same as the rear and usually only a locking diff if it is installed as a custom add-on.

Differentials allow the two wheels on the rear end, or front end, to rotate at different RPM's for turning corners. Otherwise, like during a right turn, your left wheel would need to turn more and the axle would snap. Train engines don't need them because they barely turn at all. What you experienced is the drawback to having a differential.

Contrary to what bluemazdatruck1995 said. Open diff (spider gear type) does not have one particular drive wheel. Both wheels will drive as long as they have good traction. If either one loses traction as in your case (ice), that wheel spins and little to no power is transferred to wheel with traction. Most vehicles are this way unless equipped with limited slip diff (posi-traction). A four wheel drive with open diff, say with both driver side wheels in mud/ice will spin those two wheels and not transfer power to opposite wheels (passenger side).