With Apple’s release of iOS4 for iPhone and iPod Touch we finally received multitasking, a feature requested since apps became available. However, if you’re not paying attention, you can quickly find yourself with 16 apps open, with no obvious way to quit them.
You activate multitasking by double-clicking the Home button at the bottom of your iPhone or Touch. This sends the active app into a sudo-hybernation mode. You can access those opened apps by double-clicking the Home button at any time have the multitask dock slide up from the bottom of the screen and display the open apps. Swiping to the right will show you up to 4 screens of open apps, all using battery life – though only a bit.
I’m not sure why Apple didn’t make it more obvious, but you can quit those apps simply by pressing and holding your finger over any app icon until a circular red icon appears on each icon. Clicking that red circle will close the apps. Press the Home button one more time to resume working.