The TestFlight app allows testers to install and beta test your app on iOS, tvOS, and watchOS devices. Testers must receive an invite directly from you before they can begin testing with TestFlight. Once testers accept your invitation, they can install, test, send feedback, and get updates of your beta app.
To use TestFlight, you upload your app to App Store Connect and then use App Store Connect to invite testers. Optionally, distribute your app to internal testers (your App Store Connect users) or external testers (users with email addresses). If you invite any external testers, your app is submitted to Beta App Review.
Apple provides a report service that allows you to view crash and energy reports directly in Xcode for apps distributed using TestFlight.
For more details, go to TestFlight beta testing overview in App Store Connect Help and TestFlight on the App Store.