Use the Site Settings plugin to create admin fields for storing short text snippets for use in your theme templates. For example, an email or phone number that is displayed via your header.php template.

It can also be used for storing data which you may need to reference such as the ID of a page or a post category which you use to feature posts on your home page.

Storing these settings in the admin is preferable to hardcoding them into your templates so they can be updated easily.

Read the documentation to find out how to add admin fields and sections.