Use the AutoFill pane of Safari preferences to specify whether Safari should automatically fill in forms, user names, and passwords on webpages you visit.
Using info from my Address Book card
To have Safari autofill forms using information from your address book card, select this checkbox. Click Edit to open your address book and view your card.
User names and passwords
To have Safari remember user names and passwords you enter on webpages, select this checkbox. Click Edit to view or change your saved user names and passwords.
Other forms
To have Safari remember information you enter into forms on webpages, select this checkbox. Click Edit to view your saved information.