You can make your header logo a link to
your homepage by going to Design and selecting Themes. After you select
the Theme that you want to edit, you can click Edit Header from General
Settings tab on left side of the screen or hover over the Header in the
preview window on right side of the screen and click Edit Header.
Highlight the Logo and then click the Link button.
Now go to your storefront's homepage and copy the homepage's url from the address bar at top of screen.
Go back to admin panel and paste url into the URL field of Link insert window and click OK.