Bootstrap is relatively easy. All you need to do is apply classes to HTML elements. The challenge is taking the time familiarize yourself with their vast framework.
Take the Acme website from our very first project, and throw out the screenshots. You don’t need them this time, just the content – text and images I provided. Build at least a few web pages, ideally rebuild the entire Acme website, using bootstrap. Don’t worry about style, just practice using the bootstrap grid and its CSS. If there is something in bootstrap you’d like to try out but is not included in the Acme website (like forms, tables, tabs, badges, etc. and whatever), just make it up! The best way to learn web stuff is to take what interests you and figure it out.