It's pretty simple ...
If you have a bank account linked to your PayPal account, all the buyer needs is the email address that is associated with that PayPal account. They do the rest .... once payment is made the money is transfered to that account. If you do not a have a bank account linked to your PayPal account, the money kinda sit there for you to use on another transaction, but (I don't think) you can "withdraw" it.