METHOD 1: SCREEN MIRRORING. Screen mirroring is the faster option, so we'll cover that first. Bear in mind, though, that if you're going to be streaming stuff from your computer or mobile device on a regular basis, you can save yourself a lot of time and effort in the long run by setting up a media server.
While holding the keys, press the power button. Technically you don't need to press them until it turns on, but you need to beat the gray screen, so it will be easier for you to just hold them down from the start. Keep holding. Hold the keys down until the computer restarts and you hear the startup sound (Chime) for the second time. Release the keys.