There are 3 types of currency used in Warface: Dollars, Kredits and Crowns. Each are obtained via a different method, and can be used to buy weapons, outfits, etc.
Dollars[]
Dollars is a currency is earned by playing matches and by completing contracts. You can purchase all vendor items using this currency.
Kredits[]
Kredits are obtained by purchasing with real money. Almost all weapons, outfits, etc. can be purchased with this currency. You can also purchase coins, which are used to respawn in co-op missions, VIP boosters, which can be used to boost EXP, dollar, and vendor unlock rates, and Random Boxes which awards players of certain box items.
Crowns[]
Crowns are obtained by completing regular, skilled and hardcore co-op missions within a timely fashion and with a decent score. These can be used to purchase a small amount of weapons, outfits, etc. Crowns are classed as the "best" currency in the game, as it offers items with much better stats.
All items bought with crowns will have a yellow-orange flame and streak camo on them, and provide greater stats than the dollar counterparts.