A use case is a story that explains how someone might use your product. It helps you understand what people need from your product, and how you can design something that meets their needs.

For example, let's say you're designing a new shopping trolley. Your use case might be: "Alice needs to buy some groceries. She goes to the grocery store, fills her trolley with food, and goes to check out. The trolley is heavy, so Alice struggles to push it around. She would like a shopping trolley that is easier to push."

In this example, Alice is the user, and the use case is how she uses the shopping trolley.

Use cases are a great tool for product designers because they help you understand the user's needs. They can also help you come up with new ideas for features or redesigns.