Here are two very simple background designs and one very detailed one:
For the top one, the background was re-drawn (traced back) for each page of animation! That’s a lot of work… good thing the background design was simple!
For homework, you are going to design a background for your project. You won’t actually use this one in your project, it’s just the design. So go crazy with it! Make lots of detail, color, anything you want.