You can sign up for a Google Analytics account here.

The Account Name and Website Name are for admin use to help identify your store in the event that you are managing multiple websites within the same Google Analytics account.

Copy the website tracking code from Google Analytics and paste it in the dialogue box on Shopify>Settings>Online Store>Google Analytics. Continue reading below before leaving Google Analytics.

Before leaving Google Analytics, turn on Ecommerce tracking with Google Analytics. Select ‘Admin’ from the menu bar at the top of the window. Under the ‘View’ column on the right, click ‘Ecommerce Settings’. 

At Step 1 of the Ecommerce setup, switch ‘Enable Ecommerce Status’ from OFF to ON.

Now you can track web sales from traffic source, page views, time spent on the website, and order completion.