How to redeem the key via the EA website:

1. Login here https://www.ea.com/login
2. Then go to https://myaccount.ea.com/cp-ui/redemption/index
3. Enter the key (attached to the email as a picture) and confirm it
The game will be added to your EA Account.

No EA Account yet? Register here:
https://www.ea.com/register

Download the EA app:
https://www.ea.com/ea-app