Test ordinary use and failure cases. Check a narrow screen and keyboard navigation.
Describe how information moves from input to storage to the visible list. Use any gap in that explanation as your next learning question.
Test it and explain it
Delegate
Suggest test cases and explain unfamiliar parts.
Think deeper
Judge whether the application behaves as intended and whether you understand it.
Check
Complete the main flow yourself and explain it to another person.
Put it into practice
Write a short account of one bug you found and how you fixed it.