Many iPhone problems can be effectively addressed by closing the application causing the issue or by restarting the iPhone itself. In some cases, it may be necessary to reset the iPhone or restore it from a backup in iTunes, but this is usually only necessary for severe issues.
Users with iPhones running Apple's iOS 7 or 8 operating systems can close unresponsive apps by double-clicking the phone's Home button, then selecting the unresponsive app in the preview menu that appears. Swiping upward on the unresponsive app forces the program to close. Restarting the app from the iPhone's home menu after forcing it to quit often resolves many intermittent problems with apps.
If it is not possible to force-quit an application, restarting the iPhone by holding down the phone's Sleep/Wake button is usually the best course of action. In some cases, it may be necessary to hold down both the Home and Sleep/Wake buttons to force a restart. If this type of issue occurs again with the same program, it may be useful to check the App Store for updated versions of the app; while many apps update automatically, this may not occur if there is a problem. If all else fails, using iTunes to restore the iPhone to a previous backup or factory settings is often the best solution.