If you don't want to download the tool then you need to follow these steps:
Windows 8 and Windows 10
Press Windows Key + Print Screen at the same time to capture the entire screen. This image will automatically be saved to a Screenshot folder inside of the Pictures library.
Сlick the Start button → All Programs → Accessories → Snipping tool. Open the program, click New, select the area of the screen you would like to capture, and then click Save.
Press Shift + Command + 3 at the same time to capture the entire screen and save the picture as a file on the desktop.