I would like to know the basics, and the advanced of Region3. I've watched tutorials, written notes, but I still don't understand it fully.
You can imagine region3 as either a cube or a rectangular prism that you can create by giving it two vector3 values which will end up being points from which the rectangular prism is created from, one being the very top left and the other being the very bottom right
It's usages are usually just taking the place of the .Touched event and sometimes raycasting, so it can be used for anything from hit boxes to detecting what area the player is in. It also has a lot of functions (such as PartsInRegion3 either with or without blacklist/whitelist)and events which make it super easy to use.
I hope this helped you understand it a bit more.