Adding descriptions to registration items can be done from the edit screen for that item. To add a description to a registration item, navigate to Registration and then Items.
Adding a Description:
Click the pencil icon on the desired item.
Find "Description" input on the General tab and enter the description for the item.
Ensure that the "Display Item Image & Description" is enabled.
If not enabled and a description is submitted, it will not be displayed.
Click "Update Item" to save.