Hi Betazero
We have a page here with some simple instructions on how to get started.
The geometry code is in its own branch in the repository, so go to https://github.com/EpicGames/UnrealEngine and select Branch: dev-geometry. If you’re not familiar with git, don’t worry; you can download the entire tree as a .zip file (go to Clone or download -> Download ZIP), extract it and just build it directly from there in the usual way.