To add the Free Shipping option to certain items:
Go to your Control Panel > Configuration > Settings.
Once the Settings category opens, click the Free Shipping Icon option.
You will be presented with different settings:
Icon URL: If you do not want to use the default image for Free Shipping, you can use a different image by entering the new URL of the image you would like to use.
Icon Alt Text: This is the text that will appear when you hover around the Free Shipping image.
Enable for all products: will enable the Free Shipping option for all products on the catalog, by default this option is off.
Enable products: You have the option of adding the Free Shipping option to the products you select.
Cart Price Total Threshold: In here you can add a minimum amount needed before the Free Shipping option is available.
Country Eligibility: In here you can add the countries that the Free Shipping will be available for.