Checkout Buddy offers several checkout customizations, the 2 main ones being blocks and functions (third being checkout branding customizations).

Blocks make use of 1 or more of Shopify’s checkout UI extension components to display a widget, or “block”, of UI within the checkout, thank you, and/or order status pages.

To use them they must be added to checkout using Shopify’s checkout editor, as described in How to add a block to checkout (Shopify Plus required).

Functions on the other hand, depending on the type used, modify checkout and do not need use of the checkout editor. They are active once they are created and inactive once they are deleted.