To install beta apps from an invitation email on your iOS device:
1. Open your invitation email.
2. Tap Start Testing in TestFlight.
3. Tap Accept, Install, or Update.
To install beta apps from an invitation email on a different device:
1. Open your invitation email on the other device.
2. Tap Start Testing. You will be taken to a webpage with a redemption code.
3. Open the TestFlight app on the iOS device or Apple TV you would like to test with.
4. Go to Redeem and enter the redemption code.