You can add a custom logo to your store by going to "Site Settings" under "Site" in the left menu. Click "More" and to find the image upload options. You can then select a file or drag and drop your chosen logo.
Consider using a .png file with a transparent background if your logo should sit directly on the background of the site. You can then alter your site colour scheme without altering your logo.
The logo will show in the left side of your store’s header and will automatically link to the store’s homepage.
If you do not enter a logo, the store name will appear in html text.
Favicons are the images that appear on the tabs of some browsers. You can upload your own favicon by going to the ‘Actions’ menu on the ‘Store Settings’ page and clicking the ‘Add Favicon’ button.
The shortcut icon is displayed in iOS when a web page is saved as a shortcut on the homescreen.