I’m trying to learn how to use this software but I have to search through multiple sources just to learn the latest changes. The geometry brush has been moved to the BSP, and so forth.
The video tutorials don’t even mention how the coordinate system is different from other 3D programs. I don’t know where to find details like which measurement unit it uses for scale.
Sorry you’re experiencing frustration with the documentation. Since there are a lot of avenues you can pursue to find the information needed for UE4, it can be overwhelming. However a good place to start is searching in the official documentation located here: https://docs.unrealengine.com/latest/INT/Search/index.html?q=Units&x=0&y=0 From there you can select just “Documentation” to narrow your search to the official documentation which is actively being kept up to date as much as possible.
For instance, a quick search on this page lead to an immediate answer to your question regarding Unreal Units: