When you have a website you should not just let it sit there but you should really use it to your advantage. In order to do that it is good to analyze what is happening on your site, which pages people visit, how long they stay on your site, which blog posts are very popular, where your visitors are coming from etc.
Squarespace in itself provides a very good analytics section (When you are logged into Squarespace you can find an Analytics section on the left) where you can see how many visitors your website gets, where they are coming from, what your popular content is and they even provide an exact activity log.
However overall it is limited and Google Analytics gives you a much more detailed look behind the scenes.
It is super easy to set up on Squarespace and will take you only 5 minutes without needing to find and copy any code!