The Customizer allows you to edit site settings whilst previewing the changes. A number of WordPress and Theme features are available to be edited. Some of the ones we support are listed below under the 'Related Features' heading.
To access the Customizer you can either:
Whilst viewing the actual website - click on the 'Customizer' button in the admin bar at the top of the page.
When in the WordPress Admin, you can access the Customizer through the Appearance → Customizer menu option.