Hey, finally managed to finish it.
I got a google doc for you, explaining how stuff work and a video.
Here’s the doc: https://docs.google.com/document/d/15SE-9UviwNtzPDeXGKbmEs_hgeXaScpX5HMovUWBrLo/edit?usp=sharing . Couldn’t write here everything, cuz there’s a limit. :<
And here’s the video: Gravity stuff BP Show - YouTube
I’d suggest you read the doc first so you get an idea of what’s going on. Or just go through them at the same time. 
Good luck with it! 