You can add a custom field to the Contact object to record details not readily available in the standard existing data entry options.
- Under App Setup in gray left-hand setup menu bar
- Choose Customize
- Select Contacts
- Click Fields
Scroll down past the Contact standard fields to the Contact Custom Fields and Relationships section. Select the New button.
Specify the types of information that the custom field will contain. Select the data type for the field to be added
Select the profiles to which you want to grant edit access to this field via field-level security. The field will be hidden from all profiles if you do not add it to field-level security.
Select the page layouts that should include this field. The field will not appear on any pages if you do not select a layout.
The field will be added as the last field in the first 2-column section of these page layouts. To change the location of this field on the page, you will need to customize the page layout.
When finished, select Save if you are done; or select Save & New to create more custom fields.
As mentioned, the field has been added as the last field in the first 2-column section of these page layouts. To modify the location of this field on the page, select Edit Layout.
Click and drag the new Contact field and drop it in another location.
Alternatively, select the layout name to make changes to other page layouts as needed.
Select Save to save changes to Layout.
The new field has been moved to the desired location on the layout and is now reflected on the Contact detail page.
For additional custom field attributes information, see these Force.com articles: