Yeah, I'm using OBS as well, because I also stream, but my recording quality is not that great. Mostly because my machine is not up to scratch. 

but I was also more curious about the editing bit afterward, like how you add music overlays and cut and snip the video and stitch parts together, how do you do the fast forward thing etc?

I downloaded some other free video editing tools for windows (Lightworks? OpenShot? etc) but they take forever to process the final video at the end and they increase file sizes!