Steam Trading Cards are virtual cards earned by playing games on Steam. Sets of cards can be turned into game badges and tradable Steam community items.
Foil cards are significantly rarer and more costly than regular cards. They can be used to craft the special Foil badge. Otherwise, Foil cards serve no different purpose than regular cards.
Because Dota 2 is a free-to-play game, players do not receive free cards like most other games. Instead, a card drop becomes available for roughly every $9 USD spent on cosmetic items in the Dota 2 Store.
If you have card drops available, they will appear automatically in your Steam inventory as long as your Dota 2 client is open.
Cards drop approximately once every 15-60 minutes.
Once a player has collected a set of 8 cards, a badge can be crafted on the Badges page in their Steam Profile. Badges can be leveled up by crafting repeatedly, with each set raising the badge level by one. The Foil badge can only be crafted with a set of Foil cards. Badges can be featured on your Steam Profile.
Crafting badges will always grant the player a Dota 2 Profile Background and an Emoticon, with a chance of obtaining a Coupon. It will also contribute 100 XP towards your Steam Level, which will add features to your Steam Profile display.
Emoticons can be used in chats and comments on Steam. They cannot be used in the Dota 2 client. They can be sold and bought on the Market, or traded with other players.