Always start with needs. Get yourself a project to work on or manufacture one for yourself.
Then learn the skills as necessary to complete the project.
Say you want to start off with a brochure website for a company. Something somewhat simple. You'd probably start by doing graphic design / UX design all at once whether its in a software application or on a white board or piece of paper.
You'd probably then start with empty markup. Then you'll want to start implementing CSS to style it to match your sketches.
Finally you refine, test, criticize and get others to criticize. Then you refine, refine, refine. Now you're working in UX.
As for things like Bootstrap, you kinda have to make a decision like that during the initial stages. Do you want to follow some existing framework / template? Then start your sketches based on that framework and concept. Still do you sketches but then you'd want to start the markup and css taking the framework into account.
And this is really the case for any career / skillset not just web design. Anything you're trying to learn is best done incrementally on a needs basis. The hard part is pushing your concepts to include needs you might not already know how to implement.