Install TestFlight app
Install TestFlight on your device: https://itunes.apple.com/app/id899247664
Once it's downloaded, open the application, and sign in with your Apple ID credentials to get started.
When you first launch the application, and have no invitations to join a beta testing program, the application will appear empty.
Open Apple's / TestFlight's email on your device using Apple's factory installed mail app (won't work with Google Mail app for example)
Clicking View Update will open the TestFlight application installed on your device.
If you're already signed into your Apple ID in TestFlight, the beta application will automatically be added to your account.
Install test app
Once you've accepted the invitation to be a part of a TestFlight testing program, you'll see the app you accepted appear inside of the TestFlight application on any of the devices where you're signed into the same Apple ID.
To install the latest version of an application, select an app to install, then tap on the "Install" button. Once it's installed, the "Install" button turns into an "Open" button
Just like with the iTunes App Store, the beta version of the application will be placed on your home screen -- and after downloading, it will be installed and able to run on your device just like any iTunes App Store app.
When you pressing on the app you will see the details of things to test.