Go to Setup > Click Custom Fields section > under the contact tab > Click Add
In the Add Custom Field - Contact window, select a field type and click Next
In the Configure Your Field section:
Label*: This is the field that will be displayed on the screen.
Required Option: An asterisk* will be placed next to this field if this is required.
Default Value: Enter any default value if this field must be initialized when placing on the screen.
Active Option: Uncheck this if you do not want this field to show up on the screen for any reason. All active fields are available to be placed on the screen.
Visible by Default: Select this if you want this field to be associated with the screen by default. In order to organize the fields properly, this should only be selected when this field is required for all the contacts.
Description/ToolTip: The description entered here will be presented as Help text for the user to know what this field is about.
Once the information has been filled out for your custom field, click Next
In the summary section, this will allow you to review the properties that were set up for custom field you created.
Click Save to create the custom field.
If you need to go back and make changes to the custom field, click the back button.
You will now see the custom field added to the list under the contact tab in the custom fields section under Setup.
Your All Set! You have now created a custom field for a Contact.
To associate a custom field with a contact, Click HERE