"Customize" is where you style your website and see changes live with more than 250 settings.
You can style the menu, mobile menu, site title, mobile site title, tagline (title underneath site title), links in texts, project thumbnails, project arrows, background, search, mobile spaces and you can set the frontpage.
Click "Customize" to access the Customizer.
On the left you can discover all of the settings. On the right you see your website.