Total Football cards can be earned in the application, for free, by playing matches and completing challenges. This progresses you along the Total Football pass and earning rewards for each step.
You can also claim a free pack from the in-app store page. This is available periodically and a timer begins once you claim your free pack. Once the timer ends, a new free pack becomes available.
You can also optionally purchases more packs of cards with virtual currency purchased via your store provider (e.g. Google Play or Apple App Store).