To begin your career as a coach in Mr Football, you are given a number of packs which are limited to a specific subset of positions. This is the only time you will be able to open such packs.
You will receive one midfielder pack, one backs pack and one forwards pack containing 10 cards each, plus a rucks pack with three cards and a utilities pack also with three cards. Each of the packs has a guaranteed four-star player, with a small chance of more four-stars or even a five-star card.
This gives you an initial squad of 36 players, which along with your initial allocation of trainer tokens should be enough to get your first team of 22 players in position so you can start playing and developing them.