Cards are actions which are not specific to your current location. They appear based on various stats. There are two parts to cards, the deck and your hand. Both your deck size and hand size is variable, and can range from 1 to 3. Depending on your current lodgings, you will gain a better deck or hand size.
When you have cards in your deck (one card is dealt into your deck every 10 minutes), you can deal them into your "hand", next to your deck. It is your choice whether you activate a card or not, but be warned that cards with a red border are auto-fire cards. You will get the weal and/or woe of the card immediately.