Can apps connect to internet even if I don't use them?

Unless I force stop the apps are they still active in background?

VLZ yes they can, especially those relying on notifications which can wake the app, but not all of them do.

Is profiles only way to isolate the apps? I also heard of 'app communication' too.

VLZ you have the option to turn off network permissions for any app

wildworld23 except for majority of preinstalled apps