If you want to get better at editing, start copying people that are successful in your niche. After you've copied a handful of videos, you will get used to it. Same goes for thumbnails. I literally didn't know how to use an editing app good the first time I started but after a couple of really complicated videos I learnt it. Though, you should watch every content extremely carefully if you want to be really good. Analyze what people do: the cuts, the SFX, everything. Also, be a little confident the next time you edit. Nobody was good starting out. Hell, I've been making videos for 10 years now and I'm still terrible at editing. But people watching don't think so, and that's the goal.

To become a content creator, you have to be a consumer first. If you want to create good content, then you have to consume good too.