Begin by getting whatever you want to take a screenshot of onto the screen of your Windows Mobile device. This could mean browsing to a particular website or simply getting to the right screen in one of your apps.
Press the Power button + Volume Up button at the same time and hold them for a moment. Your screen will flash slowly. This action will automatically save the screenshot in the Screenshots album in the Photos Hub.
If you are using Windows Phone 8, press and hold Start (Windows icon) and press the Power button at the same time.
Windows Tablet: Press the Windows Logo button + Volume Down button at the same time and hold them for a moment. When the capture was successful, your screen will dim briefly. Your screenshot will be saved in the following folder: This PC > Pictures > Screenshots.