Your screen will dim, and a toolbar will appear at the top: Rectangular Snip: Draw a box around what you want. Freeform Snip: Draw any shape. Window Snip: Capture a specific app window. Fullscreen Snip: Capture the entire monitor.
If you want to capture everything on your screen instantly, the old-school method still works. Press the PrtSc (or Print Screen ) key. copy screenshot to clipboard windows