You are watching a video tutorial, while also working with another app, whether it's taking notes on a word processor, or you are learning how to work with that software. Your instructor may have gone too fast, or you got a bit distracted, so you need them to Repeat what they said. The solution is simply to just grab your mouse, click on the browser window, tap the left arrow key, then grab the mouse again to refocus on the program you were working on. It's a simple solution but you are finding it happening often. It is disrupting your learning rhythm and it's taking much longer than expected to complete each course, if you do at all.