Answer 1

Well, one the most important aspects of any programming language is syntax. It's a fact: to give the computer instructions you need to know how to do that in that language.
Another thing about JS in particular is that it is a dynamically typed language. It's an important language feature and a quirk at the same time. Keep that in mind when you code and debug.
Also JavaScript works along with other technologies and languages like HTML & CSS. Learn how to manipulate the DOM and how event handlers work. Happy coding ☺!

Answer 2

1. OOP
2. functions
3. DOM management
4. EVENTS handling