For example: if you apply a contract card to a silver player, he will be able to play more matches according to the grey rectangle of that contract card, no matter the category of that card. The fifa 16 points numbers inside the coloured box of contract cards represent how many extra matches players or managers can play if you apply them that card.
The number of matches that a player/manager card has can not be higher than 99. You can apply contract cards up to a maximum of 99 per player/manager. It is also not possible to apply contracts to players on loan.
Anyone that plays a match spends a contract, even if he started the match on the bench. That’s why you should avoid to make many substitutions.
It is advantageous to apply a contract card of the same category of the player card. However, it doesn’t need to be like that. For example: you can apply a bronze contract card to a gold player.
The big trick is not do not spend a lot of fifa 16 coins on contracts but store managers in your club that give you a bonus up to 50%. Furthermore always study the relation price vs amount of matches. Sometimes a silver contract card may be the cheapest option for your gold player.