HTML and its secrets with javascript

I'm on **HTML **that I'm getting tired of studying tags and at a certain point I encounter the world of Javascript (JS)... I don't deny you love at first sight. On the other hand, I can't deny that with simple functions you have the ability to change text. BUT we want to talk about the fact that you can introduce a style to your id?!. You can change spacing, text color, even family. So from a simple html sheet I have the ability to create a JS inside it is awesome. Yesterday I studied the background of js, but reviewing the front end gives you emotions that another job wouldn't be able to give you. Can you guys give me some pointers on how to make the most of it? To use this thing to its fullest?