First, you'll need your property ID from Google Analytics!
To add it to Givecloud, go to the left-hand navigation panel and select Features > Website > Configure.
Go all the way to the bottom of the page, and at the very bottom, you'll see the 'Google Analytics Tracking' section.
There you can enter your Property ID. Your Property ID is in the format UA-XXXXX-Y. How to find your Google Analytics Property ID
Once entered, Givecloud will notify Google of page hits and purchase/donation conversions using ecommerce tracking.
If you would like to add additional conversion scripts that will run after a purchase or donation completes successfully, you can do so in Features > Website > Site Design - Advanced, in the Conversion Scripts panel.