If you're looking to quickly and easily turn off your iPhone, there's no need to fiddle with the Settings app or fumble around with any buttons. To do so, simply press and hold down the power button for 5 seconds. You'll see a slider appear on screen; slide it to the right to shut down your iPhone.
If you need to force restart your iPhone (for example, if it's become unresponsive), you can do so by pressing and holding both the power and home buttons for 10 seconds. After 10 seconds have elapsed, release the power button but continue holding down the home button until you see the Apple logo appear on screen; at that point, you can let go of the home button and your iPhone should boot up as normal.