First, if you're using Squarespace or Wix, I recommend following their step by step instructions as it should be built in. It should be in your dashboard, usually under "analytics". If you can't find it, I'd recommend googling "squarespace google analytics" and it should get you where you want to go. Wordpress users are better off installing the google analytics plug-in and following those step by step instructions.
Otherwise,
1. Create a Google Analytics account by visiting the Google Analytics website and signing in with your preferred Google account (I made a throw away one).
2. You'll click "get started" and then "start tracking". Set up your property (your property is your website)
3. You're going to be tracking "web" so choose "web".
4. Accept the terms and conditions (Read through them) and click "Get Tracking ID."
5. Install the tracking code on your website by copying the tracking code provided and pasting it into the HTML of your site. Google will tell you where exactly to install it.
6. Ensure the code is installed correctly by visiting your website and checking the Real-Time reports in Google Analytics to see if your visit is being tracked.
7. Begin analyzing your website traffic by exploring the various reports available in the Google Analytics dashboard.
There's a lot of software out there - some is great, some is meh. I'm trying to remember the name of a software I used that created snapshots and heat maps. Basically, a snapshot would record random visits to my site and I could see how a user was interacting with it and could filter it based on location. It also measured "heat" which basically meant where the majority were spending their attention on any given page. After enough data, I was able to tweak my website and I made the decision to remove my photos/gallery. Reason being, I have photos on every single page of my site and yet it was the most visited page after the homepage with an average page time of 8+ minutes. You don't have to be a rocket scientist to know what that means. Now, whenever anyone clicks "portfolio" on my website, it forwards them to a paid subscription site to see more.
I hope this helps!