I use Premiere Pro and occasionally Davinci Resolve. I wouldn't recommend either for anything simple. The native GoPro software isn't too bad?

I use Sony Vegas - works well, a lot more simple than Premiere etc. As mudduard said, have you tried GoPro's own software? That's often fine for the basics. 

Premier Elements is about as easy as it gets, if the GoPro software isn't enough for you. Costs about $100. Magix is more powerful, reasonably priced, but more difficult to use. There's also an open source video editor, but it's more limited and more buggy.

Expect there to be a learning curve. It's not super difficult, but it's not super easy either.

The GoPro software should be good enough for "simple training clips"...otherwise if you have a Mac, use iMovie. 

Either option would give you decent output for zero investment. 

Vegas often comes up on humble bundle for cheap and I have friends who seem to like it.

What framerate are you recording at? I cant get premiere to work with anything above 60 properly