Install the extension in your Chrome browser from the Chrome Web Store.
Visit the Chrome Store Listing to Install
Once the extension is installed, right click the extension icon to the right of the Chrome address bar and select "Options". Enter the Subscription License Key and click "Save". You may need to refresh Salesforce formula pages for the update to take effect. Now you can use the extension!
If multiple users were purchased through one subscription, each user will use the same license key.
You can visit the Manage Subscription page at any time to make changes to your subscription.