Screen mirroring (sometimes called screen casting) allows you to mirror your mobile device’s content to a secondary display which could be a laptop, PC, your TV or any other screen. You will need to open the connection for screen mirroring on both your smartphone/tablet and your PC/TV in order for the connection to work successfully.
Why mirror your screen? There are plenty of reasons. You might be a developer in the middle of coding and want to check your app without having to constantly reach for your phone. You might want to share your pictures on a big screen without uploading them. Or you might need to give a presentation quickly while the projector is connected to a PC.