@bobross It’s not really possible to give a thorough and detailed answer as every one learns in different ways and at different speeds.
I wouldn’t worry too much about understanding a concept fully before moving on, but you should feel as if you have a basic grasp of whatever topic. So for example, if there’s a video about types, then you should understand what a type is and an example of some (string, bool, int, etc) before moving on.
That being said, don’t worry if you do move on and think you’ve moved too quickly, as you can always go back and refresh your memory and understanding around a particular topic before moving on again.