- Enable the profile module:
- In administer » modules select in the 'Enable' column where you see:
profile | Support for configurable user profiles.
- Navigate to the administration area: administer » settings » profiles
- Select a form field type under 'Add new field'
- Follow onscreen instructions for configuring this field, and 'save field'.
In D6, additional profile fields are managed at admin/user/profile ("Administer » User management » Profiles").