When I started using THREE.js, I did not had any previous encounters with it. I learned it just from using the docs. Asking your question: you should look at the tutorials / examples given in the docs
You can also find every class / member + some explanation in the docs too. Many beginners do not know how to read it, so they need stuff like Youtube videos. If you find yourself in that category, I recommend you to learn how to read the docs in the first place, you won’t find it worthy until you learn it. Most docs for any given lib is following kinda the same structure