Using the Customizer, you can modify certain parts of your website. When you click on the Customize menu option you’ll be shown the various theme options that you can change. Depending on the theme that is currently in use, you may see more or less options than those displayed in the following image.
Clicking the small arrows will open and close each of the panels, giving you access to each of the various options. You’ll find that some of the options in the Customize screen are also available via other menu options. As an example, you can change the Site Title and Tagline within the Site Identity panel in the Customizer, as well as by using the General option under the Settings menu.
As you make your changes on the left-hand side of the Customize screen, the live preview on the right-hand side is automatically updated. You can also use the live preview window on the right-hand side of the page to navigate around your site.
By default, the Customizer will show your homepage in the preview window. Not all Customizer options affect the homepage though. You’ll find that some options in the Customizer may also affect other parts of your site such as your blog, or static Pages. You can browse around your site in the live preview window to view these other pages, just like you would when viewing your site in a separate browser window.
Until you click the Publish button, only the theme preview is updated, not the theme on your live site.
By default, your changes are published immediately when you click the Publish button. By clicking on the small cog icon (
) next to the Publish button, you can also elect to save a draft of your changes, or have them automatically published at a later scheduled date and time of your choosing.
To help with testing your site across various devices, the Customizer also allows you to preview your site in mobile, tablet and desktop views. At the bottom of the Customizer panel, click one of the view icons ( 
) to change your site preview so that you can get an idea of how it will display on a regular desktop, a tablet or smartphone device.