Rookie question: About JS Frameworks and Libraries, use'em all, or stick to one?

Hi all,

I am just getting started with JS.
I am ok with HTML5 & CSS3. From time to time I make use of JQuery and Bootstrap, except I basically just integrate/adapt already made scripts into my HTML code.
I'm just a tad confused when it comes to Bootstrap, Angular, JQuery, etc.
Apart from pure JS, which of these frameworks/libraries should I focus my attention/time the most?

Thanks in advance,

JDL