Google Analytics is a free service from Google that will capture data about visitors to your website. This helps gain insight into your website visitors for a number of benefits. The first step is to create a Google Analytics account. The next step is to integrate it on your website. There are a number of ways to do this.
Some WordPress themes have an option to add a tracking code. If so, just add the Google Analytics tracking code to your theme.
Another option is to find a WordPress plugin that will integrate the Google Analytics tracking code into your website. There are a number of plugins:
Another option and the one I recommend is a plugin called Head, Footer and Post Injections. This plugin allow you to add any tracking code and not just Google Analytics. This becomes useful if later on you need to add Google Ads or Facebook Ads tracking codes.