Not sure how to install bootstrap theme

I'm a complete newbie to CodeIgniter and PHP and I'm watching this video which is helping me to build my first CodeIgniter app.

https://www.youtube.com/watch?v=I752ofYu7ag

At around 15:57 of the video, I'm very confused about how to install the bootstrap theme in the project. The code on my header.php page is fine, but it's not clear how to install the theme.

Can someone help?

@ronniebel,

By doing a quick preview it appears that he does not install it (it being the CSS file) in the project. He references it (using it form the bootswatch.com web site). If you wish to actually download it then try this link: https://bootswatch.com/help/

Problem solved. It was happening because the css file it references doesn't exist any more. Got the correct one now.