How to turn on orientation lock on iphones

This is extremely* simple, but a lot of people don't know how to do it.

    
STEPS
TOOLS

Double Tap the home button to open multitasking.
Slide the row of apps to the right to reveal the iPod control buttons and the orientation lock button (farthest to the left).
Simply press the button and you're done! ^.^

 An iPhone! ^.^