After your vendor account has been approved, open the Add a Card page in your vendor dashboard.
You can search for the exact card immediately, or use the guided browser: choose a TCG, choose an expansion or set family, choose a set, then choose the card.
Click Sell Yours to open the existing listing form with that catalog card selected. Confirm the printing, condition, quantity, price, photos, and shipping choices before publishing.
You can also start from a catalog card page by using Sell Yours there.