How do I install the Shopify App?
You can install Merchant Mail through the Shopify App Store.
Go to the Merchant Mail page in the Shopify App Store and click the Get button.
You'll be asked to confirm installation of the app. Click the Install button to continue.
All done! At this point, you'll see the Merchant Mail app withing your Shopify admin site. Here, you can change settings, including the ability to link additional email addresses to your Shopify store.
Once you've installed the app, you'll want to install the Gmail Add-on.