GroovePages Builder: Background Settings
In the sidebar, the background dropdown allows for customizing the background for a selected element or block. The simplest way to do that is by choosing a color. However, you can also choose an image as the background.
If you choose to select an entire block additional options will be available in the background area. When adding an image you can blur it. However you can also add video and patterns to the background of a block. You can use all of these settings, if you choose, and they will be layered with the image on the bottom, the video next and colors/pattern on top.
Once you add an image you'll have the option to align it and add parallax (where the content on top scrolls but the background does not).