In order to efficiently work in SEO, especially for on-page work, it is crucial to use reliable data, and analytics is key here in compiling reports which will enable for instance to identify the number of visits/unique visitors and conversions for specific pages and site sections, or compare data by device type or browser.
Google offers a free version for an analytics tool: Google Analytics. Its set-up is quite straight-forward.
Activate the account by adding the snippet in the code (head section) for each page you want to track. Create Accounts / Views for each account: All Data, Test, Master Create Filters: exclude for instance all spam bots traffic and internal traffic. Create Reports and Dashboards. Correctly setup UTM for your marketing campaigns. Optimize continuously, analysing reports and acting accordingly (new reports, new filters, etc).
To get more valuable insight especially in terms of keywords, it is better to integrate Google Search Console to Google Analytics. GA itself does not show any keywords; they appear as not provided.