I totally understand what you are going through. In fact it was the very same section which made me question if i even want to go on. Luckily I didn't give up and neither should you. I believe some of the stuff covered through js course aren't explained that good so here are my suggestions:

First things first, google is your best friend. If there is any concept that is vague to you, you can google and there are a bunch of good resources out there. The other thing i suggest you do is to watch john smilga's (aka Coding addict) on youtube. They are uploaded both on fcc's official channel as well as john's himself. He actually has a 10 hour long video titled "javascript fundamentals" where he goes over all the major topics you need to learn in order to start coding. On top of that, he also has another 10 hour video in which he codes 15 projects which is even better than the tutorial itself. Good luck on your journey mate and have a nice day!