Go to Homepage>customize>Site Identity.
Logo: It changes the main logo of the site.
Site Title: It changes the main site title of the site.
Tagline: It changes the tagline (i.e. Description) of the site. Just below site title.
Site Icon: The Site Icon is used as a browser and app icon for your site. The icon must be square, and at least 512px wide and tall.
Set your site’s title, description and add logo by navigating to Customizer > Site Identity.