Um.. I've done Bootstrap a couple of time and I feel like it's mostly a CSS/grid framework.

The javascripts are there to make stuff backward compatible with older browser, such as modernizr, and whatever.

If you want to learn say web design/web development. You should learn HTML/CSS first then Javascript with DOM tree. Then jQuery after that a serverside language imo.

Dom Scripting is a pretty good book btw.

It depends on what you actually want to do with Bootstrap. Do you need it to quickly assemble a website just for prototyping and you are satisfied with the layout Bootstrap comes with? In that case: just read the Bootstrap manual and you will mostly be fine. But, if you want to make changes to the layout and have some more control, you better start of learning html and css (like all have said here).

As pointed out, you need to start with HTML. First learn the basics(class, ids, tags, data-* attributes) etc. If you haven't done HTML at all it will be slightly tricky for a couple of days. JS won't be a huge challenge.

Start with HTML. Once when you master it, go to JS. A good place to start: http://www.w3schools.com/

If you know C/C++, HTML/JS will be pretty easy for you.