Firstly there is a plugin in joomla core called User – Profile which you need to enable.
This plugin will add additional fields to the user registration form and user profile
This plugin stores the values in jos_user_profiles table, with each field being stored in a separate record
You can add a user profile menu item to allow registered users to edit their details
Now assuming a user has filled out this information, when they win an item it will show their address from their user profile
The word delivery address is a url link that allows them to edit their profile. This address information is passed to PayPal via the Pay Now button
The address in their profile at the time of the winning bid is also included in the auction item record.