To see what applications you have open on your iPhone or iPad just open the manager by double - clicking the Home button. This administrator there from iOS 5, but from that version to the current iOS 9 have been making some minor amendments to improve the user experience.
On the other hand, I must say that many users think that closing apps that do not use saves battery, but several studies have found that it is not. Anyway, if you want to close all applications at once just keep reading, because then you have two (traditional and Jailbreak) methods.
Close applications iOS
As we said before, currently iOS does not allow you to close all applications at once, but you can save closing them two at a time. Access the administrator by clicking twice on the Home button and then use multiple fingers to select more than one application and move them up. As simple as that!
If you have your device with Jailbreak tweak you can take advantage of SmartClose to close all apps at once. Created by developer Ryan Petrich, this tweak is available on the http://rpetri.ch/repos/ repo and once installed options panel is created in your Settings app so you can configure it to your liking.
Other similar tweaks to SmartClose are ClassicSwitcher or SwitchSpring. You see, you have several options to choose the one you like and suits your needs.