On the Getting started section:

Documentation information
In many of the examples shown in BootstrapVue's documentation, you may see the use of CSS classes such as ml-2, py-1, etc. These are Bootstrap v4.3 utility classes that help control padding, margins, positioning and more. You can find information on these classes in the Utility Classes reference section.

Many of the examples in this documentation are live and can be edited in-place for for an enhanced learning experience.

BootstrapVue also provides an interactive playground where you can experiment with the various components and export your results to JSFiddle, CodePen, and/or CodeSandbox.