How do you track your keywords properly?

Hi guys, I want to learn how to track the changes in rankings of our keywords. First, I'm not sure if I should track the keywords we want each page to rank for, or the keywords we're already ranking for, or both?

Second, how do we use that data? What I usually do is if there are positive changes in ranking from the 2nd to the first page or any positive changes on the first page, I check the traffic to see if there are any improvements there, too. Any recommendations about what else to do?

By the way, how do you check what keywords a specific page is ranking for in GSC or GA? I know ahrefs and SEMrush gives you these, but I'm not sure where to view them in GSC or GA. I tried checking GA>Acquisition>Search Console>Queries and Landing pages. I also viewed GSC's performance tab. But I don't see it anywhere.