I have a small black square box that suddenly has appeared on my iPad screen and I can't get rid of it. It says zoom out, full screen zoom, etc. when you click on it. I need to get it off my screen; it's driving me crazy.

You have one of the accessibility functions enabled. Go into Settings > General > Accessibility and turn Zoom 'off' (the icon that you are seeing is the 'Show Controller' on the Zoom settings screen) - and check what Accessibility Shortcut (a triple-click of the home button) is set to at the bottom of the Accessibility screen