What do I need before I can buy or sell?

Four things, and it is worth having all four ready before you find something you want:

• A Creta account, signed in.
• The Creta Wallet browser extension, installed and connected to the site.
• CRETA in that wallet, to bid with.
• POL in the same wallet, for network fees. Every step here is a blockchain transaction, and a wallet holding only CRETA cannot make any of them.

Selling needs the same, minus the CRETA: you still pay POL to list, and again to collect the proceeds.