What and how to monitor SAAS site?

Hi Everyone,

I suspect this is a basic question but the more I think about it the more down the rabbit hole I go. I recently created a site and I'm getting some traffic but I'm not sure what and how to monitor it?

I added google analytics and splitbee to get stats but I'm not really sure what to do with it. I've read about setting site-level KPI's, etc but how do you figure out the right one? I've read that you should speak to your users, but how do you engage with them if they just show up as IP's in your logs?

Can anyone suggest a resource to learn more about what to do?