Let's take a closer look at how you can install your iOS or tvOS app for testing.
TestFlight
TestFlight is a beta-testing service that is available in your Apple Developer account.
The fastest and the easiest way is to use Internal Testing in TestFlight. When your iOS or tvOS app is ready for testing, we'll upload it to your account at App Store Connect and it will appear in TestFlight.
Preparations
To start testing, you’ll need to accept an email invitation and have a device that you can use to test. To send you the invitation, you need to provide us with your Apple ID email address. If you don't have an Apple ID, you can create a new one here or you can provide us with your email address and you'll be prompted to register a new Apple ID when you will be accepting the invitation.
In total you'll need to accept 2 invitations:
The first one is to join your Apple Developer team and have the possibility to become an internal tester. That is why an Apple ID is required.
The second one is to join TestFlight and test your app.
If you want to complete this preparation step by yourself, see the following article.
Installation
To get started, install TestFlight on the device you’ll use for testing. Then, accept your email invitation to install your app.