Old-school htc way
Press power and home buttons at roughly the same time, screenshot is taken with a camera sound. Saves under Screenshots.
Android way #1
Press power and vol down buttons at the SAME time, you need to press them at the VERY same moment and keep them pressed until you hear a camera sound and the screenshot is taken. Saves under Screenshot and shows itself on notifications, where you can view it and share and such.
Android way #2
Same as above but you down do it via the quick settings menu you get to via either notification (one finger) and then press the quicksetting icon to the right. Or: Drag down with two fingers on notification bar, to end up in the quicksettings at once. And simply tap Screenshot, it will take a screenshot of the screen you was on before you pulled down the notification bar. Saves and shows in the same way as android way #1.