Most mobile apps are designed in a way that allows users to learn the interface by using it. There are only a few situations where onboarding screens can be helpful in a mobile app:

• When the app is complex. In this case, it's better to explain how to use features as users discover them instead of an instructional tutorial that can overload them with unnecessary information.
• When you need user information to get started. For instance, users of banking apps may need to create an account and confirm their identity.
• When the application functionality is tailored to users' context and preferences. For example, a fitness app might need to know a user's height, weight, blood pressure, etc.
• When important app features or workflows are unique, unfamiliar, or different from standard UI patterns. For example, car-sharing apps that have onboarding flows to explain how to use their service.

If you're unsure whether your app needs onboarding, user test the app without it. Do users struggle to use it for the first time? If yes, consider whether you may be able to make some changes to the app design first to make it more user-friendly. If that's not possible, prototype an onboarding flow and test it.