We are going to describe several combinations of hardware buttons for OnePlus X phone.
When device is powered off:
Press during several seconds:
Volume down + power --> boot into recovery mode.
Volume up + power --> boot into fasboot mode.
When device is powered on:
Volume down + power --> take a screenshot.
If we activate screenshot in power menu we can also take screenshots using power button:
Settings -> Buttons -> Power menu -> Screenshot(enable it)
Press power button some seconds, and a menu will appear: