More for you to chew on...
The power leaves the engine via a crank shaft and enters the transmission. A transfer case is bolted to the back of the trasmission. The power goes through the transmission, into the transfer case. The tcase sends it to either the rear axle alone (2WD), or both axles (4WD)- depending on if it's in 2WD or 4WD. It also can be in high range or low range.
Fancy rigs like Range Rovers have a Tcase with a differential in it so you can do 4WD auto, but they also allow you to fully lock the center diff to make the front and rear alxes turn at the same time, wheich is advantageous over rocks. They also typically have fully locking diffs front and rear- generally ARB air lockers. If you are rock crawling, you want it all locked so all 4 tires turn at the same time. Front axle, tcase, and rear axle. Individual wheels are not locked. You need more than one wheel to lock them together. An axle is locked, not a single wheel.
Low range reduces the gearing so you have a bench of low end grunt and very little top end speed. It's for crawling over rocks or pulling out something that is stuck. I've never had a need to put my truck in 4WD low. It can be probematic to get out of 4WD low sometimes as well.
Gen 1 Raptor transfer cases are simply gearboxes with an electric motor to shift it. It has 2 speeds, hi and low. It has two 4WD modes, 4WD engaged or not. That's it.
Gen 2 and 3 trucks have a more advanced tcase with the ability to allow the front and rear axles to turn at separate speeds, which is necessary on dry pavement when you turn. That is what allows an "auto" 4WD system. You cannot run in 4WD on dry roads with a Gen 1 truck, unless you are only going in a straght line.
"Lockers" are typically in the axle housings, part of the differential. If it's a fully locked differential, both wheels on the same axle turn at the same time, always. There are tons of differnt type of limited slip differentials/lockers ouy there. ARB air lockers, Detroit style mechanical lockers, Auburn cone style, Tru tracs, and Torsion style of which there are many brands. They all try to do the same thing, drive both wheels on the axle instead one- but they all do it differently. Limited slips aren't fully locked and each have major downsides when offroading. The Raptor's factory rear diff can be fully locked.
As I said in my post above, no Raptors have ever had a front locker, only a limited slip Torsion style diff. It allows the front tires to turn at different speeds in a turn, but still sends power to both wheels.