Can you recommend any resources for learning OBS?

My daughter wanted to record some videos of her playing a web-based game. I found the interface to OBS unintuitive. I managed to figure out how to capture a specific area on the desktop, but it was unexpectedly difficult to resize the output to match the input. I found some way of doing it that I can't remember.

A few months later I had to do it again and that time I couldn't find the option to resize the output to match the input.

I'd love to find some resources to help her learn how to setup OBS for recording or streaming.