1.You need to edit the size of the picture and the size is usually displayed there. Where those options are depends on your Software.

2. A frame is a border around the thumbnail. I just add 2 because it looks better.

This post will help you further: https://steemit.com/dtube/@valorforfreedom/3xnnkuzm

And don't worry about it, we are all newbies when we learn something new.