Need help understanding

Mattw112 bootstrap will essentially sell (i think they may have extremely basic free templates, too) the source html/css code. Maybe some basic Javascript functionality (I havent used bootstrap in forever) and you can just literally copy and paste an entire website into your sharepoint web part, and it will look like a modern web page. After copied and pasted, it would be an example website. so it might come with some generic picture background, all you do is change the image src for that piece of code and make it your own, or find the line of code that shows the title, and change that to your own. and that's how you can make the bootstrap template website your own. it saves you the time an effort of building a website from nothing, and allows you to simply make edits. 

to be more clear, if you go to bootstrap, you'll see picture of what different websites can look like. you choose a look, and it tells you what code to copy and paste and it'll run.