Each set of trading cards has a badge associated with it. You can earn and level up trading card badges by crafting a completed set.
To access your list of available badges click on the badges
link on the right side of your Steam profile
. Badges which require trading cards will display the card images on the bar. Cards which are greyed out are ones you need, and the ones which are lit up you currently own.
Clicking on each section will bring up additional details about the card set and resources you can use to find the ones you're missing.
Near the bottom of the page you can view who on your friends list has completed at least one level of the badge.
You can also see who on your friends list owns the cards you're missing. Selecting the buttons next to their names will allow you to send them a chat message or a trade offer. It will also provide links for the games trading forum and the Steam Community Market
page for the card.
Next to the badge name there is a "How do I earn more card drops?"
link. Clicking on this link will display information on how you can earn card drops from the selected game.
Purchasing a game will earn you half of a single card set for its badge, the others will need to be collected by trading or purchasing them through the Steam Community Market
. These cards are dropped randomly through play time, and don't replenish once depleted.
Free-to-play games such as Team Fortress 2
or Dota 2
will drop trading cards based on your in-game purchasing history. You'll receive approximately one additional card drop for every $9 USD spent. For these types of games there is no limit to how many cards you can earn. These cards are also drops dropped randomly through play time once you've met the requirements.
Once you've depleted your card drops and if you've logged into Steam within the last week you'll have a rare chance of receiving a booster pack. Booster packs contain three additional cards, and your chances of receiving one increases by 20% at Steam level 10, 20 and so on. They are granted randomly to eligible users as more badges are crafted by members of the community.
Clicking on the "How do I earn more card drops?"
link will inform you on your booster pack eligibility status along with your purchase progress for Free-to-Play games.
You can also view a complete list of games you're eligible to receive a booster packs for by selecting the "View my booster pack eligibility"
button located at the top of your badges page.