In one sentence, describe what the following article is about:

It's a gray app with gears pictured that can be found on your Home Screen. It's located in the upper half of the page. It's in the upper half of the page. It's listed under the "Vision" heading. You'll find it at the bottom of the screen. You will see a check-mark displayed next to it. The entire screen will zoom in when you activate the zoom feature. It's in the upper-left corner. It's the big circle located at the bottom of your phone screen. It's blue and has the the letter "f" in it. Sign in with your Facebook password if necessary. You'll need to perform this action quickly in order for it to work. You will be zoomed into the full screen.  Tap the screen twice again, with three fingers, to zoom back out. To read the content that's being magnified, use three fingers to scroll side to side and up and down. To zoom in further or zoom out, triple-tap the screen with three fingers; a menu of options will appear. Drag your finger on the line with the two magnifying glasses to the desired zoom level. Moving it to the left (toward the magnifying glass with the "-" inside) will make content on the screen appear smaller. Moving it to the right (toward the magnifying glass with the "+" inside) will make content appear larger. Tap anywhere outside the screen to close the menu of options.

Summary:
Open your iPhone or iPad's Settings. Tap General. Tap Accessibility. Tap Zoom. Tap Zoom Region. Tap Full Screen Zoom. Tap the Back button. Press the Home button. Open the Facebook app. Tap the screen twice with three fingers.