Sigil: City of Doors

Where can I learn how to play the card game on this server?

Khazeets gives out a normal deck, so ask that NPC. Just find another PC with a deck and setup a table by clicking on the deck then marking a spot. Click on the table and it will ask you to wait for the other player. Once the other player is connected, then it comes up with a menu to select the rules which I am still learning, once ready click it to make it yes. Then the card game begins. Best way is to try it and its pretty much explains its self.

OK. Thank you. I will try it out.

New cards drop as loot. How critical are those cards to having a good deck?
Can you build a totally custom deck, or can you only add cards to the base deck Khazeet hands out to players?

You start with a basic deck from Khazeet, then build upon it with cards you find. So everyone starts the same but you add cards to your deck from what you find.