Usability testing helps improve your mobile app by finding problems real users face. First, set clear goals, like checking if users can easily find features. Then, choose people who match your target audience. Give them simple tasks to try on your app. Watch how they use it and listen to their feedback. Look for areas where they get confused or stuck. After the test, review what you learned and fix the issues. This helps make mobile app UI design easier and more enjoyable to use.