There's no point in building a website if it's not being visited and, more importantly, delivering the right information and functionality to your visitors. Monitoring the activity on your website can help you understand why and how people are finding and using your site, and also help you make informed decisions about changes that you might want to make in future.
You can carry out basic monitoring and analysis using Squarespace Metrics, which is Squarespace's own built-in statistical reporting tool. You can find out things like:
The number of visitors your site receives, on an hourly, daily, weekly, or monthly basis
The number of pages viewed, and the relative popularity of each page
The words that people typed into search engines to find your website
Which websites are linking to yours, and how much traffic those links generate
You can access Squarespace Metrics in the Metrics panel, accessible from the Home menu.