Believe it or not, quitting apps and closing apps are not the same thing. This is another one of those quirky things about Apple products that you might not ever know about until someone shows you.
When you are finished using an app and press the home key at the bottom of the iPad, you are now out of that app and back to your main screen. What you may not realize, though, is that you actually haven’t closed that app. Not a big deal and nothing you have to worry about until those open apps really start to stack up. At that point you could be taxing the system and start to encounter some problems. Apps might run slowly or quit unexpectedly, or you might find the home key doesn’t respond anymore at all.
To see your still opened apps, press the home key twice quickly. A screen will pop up at the bottom showing all of the apps you have been using. It might show all of the apps you have EVER used. No worries, just press and hold on one of those apps. They will all start to wiggle and now you can press the minus sign on the top left corner to close them out. Do this one by one for each app until you have closed them all.
This also applies to iPhones and iPods, so if you have one of those and press the home key two times, you might be surprised to learn just how many apps are open and waiting…