When you see something you like, you can buy it right away using "Buy it Now". You can also make an offer on the item (you will have to sign-up or log-in to the site). When the seller accepts or counters your offer you will be notified via both email and through Grailed messages. You will be sent a link to check out using PayPal. The seller might have accepted multiple offers so act fast. After sending your payment through PayPal you will be directed back to Grailed.
When you click "Pay with PayPal" there's a prompt underneath the PayPal login to check out with credit/debit card. You can use that to pay directly by card instead of using a PayPal account.
Please note that purchases made through PayPal's guest checkout are not eligible for Purchase Protection. You must create a PayPal account to qualify for purchase protection.