What kind of scenario Can I use and apply while applying design-patterns to my project?

Currently we study design-patterns in Java. Our professor gave us assignment that we will make a project which I will apply 3 design patterns into our project. The patterns that I will use as follows

-Strategy Pattern -Observer Pattern -Singleton Pattern

I choose my project as library system that it will be an Android application. Here are a picture of existing Java Classes in my project . Library Management System Classes

I can make this Android application but I am lack of producing scenario for my project but I don't know how to apply these design patterns to my project I will be happy if you give me any suggestions or any source for this. Thanks in advance.