To get started with CPT modules, you need to select the post type first. You can select the post type from here-
CPT Module > Content Tab > CPT settings > Post type> Select a post type.
Once your post type is selected, then you need to add a new item or element. Divi CPT modules offer 11 different elements to choose from.
Add a new element from here-
CPT module > Content > Plus Icon (Add New Item)
Once clicked, you will be navigated to the child Item, where you can add an element type from the dropdown list.
Now, select an element of your choice, and the content will show up in the visual builder.
To add another element, Click the back icon on top of your module setting interface.
Then click Add New again.
NOTE: Make sure you have at least one post published under your selected post type. If your post type doesn’t have any post, then the module will show empty.