Card Trading ?

https://www.steamtradematcher.com/ the best place for 1 : 1 Trade on Trading Cards

https://www.steamcardexchange.net best place for cross-game trading.

you can trade cards for games? Meaning cards in exchange for games?

Click the Trades link at the top of this site’s navigation to go to SteamTrades, the sister site of SteamGifts. Plenty of people willing to accept cards for games (myself included).

If you want to trade them for games, Steamtrades should be the best place. Barter offers a generic card item as well, but you can't specify them. If you just want to load them off, Oy-Vey-Keys accepts cards, but it's not much you're getting for them and they mostly offer trash games.