This is a good read about Bootstrap’s Grid system.
For the navbar you’ll want to read about it on the Bootstrap docs.
For starters if you want to make a responsive page with Bootstrap, stay away from using height, margin, padding, etc (or any CSS for that matter). When I use Bootstrap, first I’d use the Bootstrap classes to style/layout my page (those alone can work wonders 
). Then I proceed with changing colors, fonts, etc. Try to avoid adding pixel-based margin/padding to your <div>s, especially on the sides (for the sides use percent-based values). And don’t explicitly set a <div>'s height; it’ll most likely break the page on small screens.