Hello. I am unsure of what render / project settings I should be using. Sometimes I get my video to come out perfect (in terms of sizing) and other times it comes out like the one you see in the link provided . I record off my monitor that has the dimensions 3840 X 2160. Is there a step by step tutorial on what best render / project settings to use for this?
Your video is 16:9 4K. You should be using that for project settings. Even better if you enter the Project Settings (on the Preview window) and use Match Media to match your project settings to your video specs.
Once you've done that, you can output your video as pretty much any 16:9 output and you shouldn't get those black letterbox bars.