In the store you are able to buy packs for real money. (On XBOX with Microsoft Points).
There are three types of packages (sometimes special packages):
In the gold packs you can pick up gold cards, in the silver packs silver cards and in the bronze packs you will pick up bronze card. (with the exception)
All cards come in from the start of a packet.
There is also a regular "make money" method where you buy bronze package and sell the content. Learn more about it here .