If you have a recent HTC phone then you probably find that there’s often a big black bar across the bottom of your screen, taking up space you spent hard cash on getting.
In a way, HTC were doing the right thing and the apps were supposed to change so that it wasn’t necessary. Other manufacturers kept the menu button, though, and so the apps never got changed.
To fix on One X: Slide down the top menu and get to Settings (in top right). Select Display, gestures & buttons, then Recent apps button, then you can choose to either change that button to be the menu button (“Press for menu, press and hold for recent apps”) or you can hold it down to get to the menu (“Press for recent apps, press and hold for menu”).
By the way, if you want a screenshot on an HTC phone, hold the power button and press Home. It should let you know that it’s worked as well.