You will have received a link to Test Flight in an email invitation. Click the link to begin the signup process. You’ll be prompted through a series of steps to prepare to test Pocket.
If you can’t find your invitation link, here it is: https://testflight.apple.com/join/JSiinnyE
Step 1 is to install the Test Flight app. Once you have the app installed, you can proceed to Step 2, Join the Beta (actually, Alpha!)
In order to join the Alpha test, just select the Start Testing button.
When prompted to ACCEPT and to INSTALL, just select the buttons.
When the install is complete, select OPEN to start Pocket.