Bootstrap is a CSS framework that makes it easier to create website and web application user interfaces. Bootstrap is especially useful as a base layer of CSS to build sites with responsive web design.
Bootstrap 3 was out for almost five years before Bootstrap 4 was finally released at the start of 2018. When learning Bootstrap you will likely come across many tutorials that cover Bootstrap 3 but not version 4.
If you are completely new to Bootstrap and CSS frameworks in general then I recommend learning Bootstrap 4. If you have already been working with Bootstrap 3 then there is no major rush to upgrade to the latest version. Bootstrap 4 is more complicated than version 3 because it has a lot more features so the learning curve is a bit steeper.
Full Stack Python is actually built with an early version of Bootstrap 3. However, this site is so heavily customized with my own CSS that I likely will never upgrade to Bootstrap 4 because there are no new features that I feel will be useful in my specific situation.
Getting Started with Bootstrap provides a walkthrough of a sample starter template so you can understand the CSS classes that Bootstrap uses. There is also a follow up post that shows how to create an effective sales page with Bootstrap 3.
What is Bootstrap and how do I use it? is an awesome tutorial that goes through many of the main Bootstrap elements such as icons, navigation bars and "jumbotron"-style webpages.
Bootstrap 4: What's New? shows a slew of comparisons for how user interface elements have changed design over the past several Bootstrap major version iterations.
How to use Bootstrap 4 forms with Django shows how to combine the popular django-crispy-forms library with Django to create and obtain user data through web forms that are styled with Bootstrap 4 CSS.
Easily deploy your Python web apps to Digital Ocean's reliable cloud computing platform.
Secure and manage identities in your Python web apps with Okta.
Scout monitors the performance of your Python apps, identifying slow queries, memory bloat, and more. Free during Tech Preview.
Upgrade your Python skills by reading Real Python's awesome programming email newsletter.