I have an iPhone 4 just downloaded Apple iOS7 tried out the apps and updated several of them, now I can’t close any of the apps. How do you close an app?
Reminder – you do not need to "close" apps on an iPhone (or any iOS device). It's not like Android where apps stay running in the background indefinitely. Some have a period of around 10 minutes where they can continue to make limited requests, such as Spotify when syncing your music, but 95% of apps you have on your device will suspend state when you hit the Home button.
There are no performance, battery or other improvements to be gained from "closing" apps – all you are doing is discarding the frozen state.
I was asking myself the very same thing this morning! The answer suggested in http://www.imore.com/how-kill-force-quit-apps-ios-7 is:
1. Double click Home to launch the multitasking cards interface
2. Touch and hold a card and then toss it up and away.
3. Touch and hold multiple cards to toss multiple cards away. (Up to three - the maximum shown on screen at any time).