Your Mac’s Activity Monitor app looks complicated, but it is a utility that you should get to know because it can be very useful. Apps like Mail and Calendar open windows on your desktop and you can clearly see what apps are running, but behind the scenes macOS runs much more. Some things never display windows and we are unaware that they are running at all. Activity Monitor can show just the apps with windows (go to View>Windowed Processes), or it can show everything (View>All Processes). It enables you to see apps that use the most CPU, memory or battery, apps that prevent your Mac from entering sleep mode and apps that may have problems. Whenever your Mac is misbehaving, launch Activity Monitor.
Developer
Apple Inc