Some applications aren't ended completely when your mobile phone returns to the Home screen. They keep running in the background unless you end them from the list of active applications and may slow down your mobile phone.
End active applications
Press the Home key twice.
At the bottom of the display a list of active applications is displayed.
Press and hold any menu item until the menu items start to jiggle.
Press the end icon to end the required application.
Return to the Home screen
Press the Home key to end the session and return to the Home screen.