Logcat is basically a “terminal” that displays messages of what’s happening in an android device. When an error occurs, it displays the message there.
On Android Studio, on the bottom left, there should be some small tabs, and one of them should be called “6: Logcat”. If you click that, it should display the Logcat of any connected device. It will display a lot of messages, from all apps running on your device, but you can filter messages per-application to make it easier to find.
So the idea is to connect your device, open the Logcat window, and keep looking at it while on your device you are installing your app to trigger the “App not installed” message. At exactly that point, Logcat should display some error message with more details.
“adb” (Android Debug Bridge) is basically a set of command-line tools to do the same thing, but without using Android Studio. No need to dive there, it is a bit more involved that simply using Android Studio.