To use TestFlight, you’ll need to be a member of the iOS Developer Program. You can upload your app binaries and import a CSV file of testers into iTunes Connect. While apps built with the TestFlight SDK will continue to function, we recommend that you remove the TestFlight SDK from future releases.
When a developer invites you to test a beta iOS 8 app, you will receive an invitation email with a link to the beta app and the TestFlight app on the App Store. Once you download the developer's beta app and the TestFlight app, you’ll be ready to give feedback. Learn more