Connecting Google Analytics with your page is extremely easy. Make sure that you already have a Google Analytics account. If you don't you can sign up for one here.
Once you're logged into Google Analytics, locate the Admin tab at the top right of the page:
Once you're on the admin page you'll need to select the "Tracking Info" tab, then select the "Tracking code" option. Doing so will reveal your unique tracking ID that you'll add to Instapage. It should look similar to the example below:
Go back to Instapage and find the Analytics button under the main page settings within the builder.
Select Google Analytics from the next tab.
Now simply add your unique Tracking ID in the field shown below:
That's it, save your page and you're done.
Note: This only tracks page views. If you would like to track more advanced metrics such as custom events with Google Analytics, please see this article: https://goo.gl/DKEUFp.