There are several resources to manage in Lost in Random, one of which is cards. You start with no cards, but you can get more as you progress in the game. Fortunately, there are a number of ways that players can acquire cards.
You can find cards throughout the worlds of Lost in Random by finding them on the map or completing quests. Sometimes you will receive cards from battle as a reward. You can also purchase them from Mannie Dex.
When you first arrive in the Valley of Dice, you will receive a hand of cards for free. After that, you will have to find or purchase them. They can be purchased with coins from Mannie Dex. When you first talk to Mannie Dex and gain access to his shop, you will have the option to open a card pack of a particular type and add those to the shop. These types are:
Buying cards from Mannie Dex spends coins and fills his coin meter. Once the coin meter has hit a certain amount, you will have the opportunity to open another card pack. Available card pack options are determined at random, but you will always have three options at a time.
For more information on Lost in Random, check out Can you save in Lost in Random? and Where to find the Storybook Pages in Onecroft in Lost in Random on Pro Game Guides.