Bootstrap is just a framework. It's a way to layout your site using a grid system, cross-platform compatible css, responsiveness, etc. It's a shortcut to writing a template by hand as long as you stay within the confines of it.
The best place to get started on the kinds of things you can do with it would be their github:
http://twitter.github.com/bootstrap/
I personally use twitter bootstrap for all my own projects that I combine with frameworks like Yii which has special extensions created to make my dev life even easier.
GL
