crimsonpython24 the active apps panel shows which apps have a service running continuously with an open connection to their server. You will likely see apps there which are used for push notifications such as GmsCompat for Google Play Services or a specific app if it uses its own implementation of push notifications, like FairEmail, for example. If you're using a VPN app, you'll see that listed there too.
99% of the time, there is no reason to touch the active apps UI. You can't add apps to that list, only stop ones that are listed. The vast majority of apps don't use the active app functionality, and work perfectly well without that. It's not intended that they should appear there.
Probably what is more interesting for you is the recent apps screen which shows all of the apps you have open in the background. For more details about that, please see the documentation here: https://developer.android.com/guide/components/activities/recents