Let's start by giving our project a backdrop. Below the stage you'll see that there are four options for creating backdrops, each of which has an icon:
Adding a Backdrop From the Library
Start by using the library. Click on the left hand icon to view the backdrops library:
Select an image (I'm using 'beach-malibu') and click the OK button.
The cat sprite will now be in front of your background:
As your project had a plain white backdrop when you started, it will now have two backdrops. You can view all of your backdrops by clicking on the
Stage (next to your sprites) and then clicking on the Backdrops tab to the right of the stage. This reveals the backdrops pane:
Here you can add or delete backdrops and edit existing ones.
Now see if you can now make your own sprite with a backdrop you have created or edited.