If you would like to offer customers the option to purchase Shipped Green carbon neutral shipments, you can enable it in the Shipped Suite merchant admin with the following steps.
Go to Settings > Shipped.
Check "Green - Carbon Offset Shipments".
Enter the requested information.
For Shopify non 2.0 Themes and Shopify Plus Legacy Checkout, add Shipped Configuration to configure the Shipped widget. See instructions here.
For BigCommerce, configure your Shipped widget here.