Flask-Bootstrap packages Bootstrap into an extension that mostly consists of a blueprint named 'bootstrap'. It can also create links to serve Bootstrap from a CDN and works with no boilerplate code in your application.

Here is an example:

from flask_bootstrap import Bootstrap
[...]
Bootstrap(app)

This makes some new templates available, containing blank pages that include all bootstrap resources, and have predefined blocks where you can put your content.

As of version 3, Flask-Bootstrap has a proper documentation, which you can check for more details.