You send them pictures of your books and a selling price. They get it sold. You get paid PayPal Friends and Family (no fee payment) or, if you prefer, Goods and Services, and you ship the book fully insured to buyer. You send them 5.5% of the sale price ($20 minimum.) They make it pretty easy. As a consigner they’ll need your name, address, PayPal address, and phone number. In order to get started selling with them, they would need a few references who can vouch for you, maybe mutual followers, big comic dealers you’ve done business with, CGC boardies, long standing eBay account, etc.