Taking a screenshot on a Mac is a simple process. However, on a Windows PC, things are a little more complicated. On Windows 10, you can take a screenshot of the entire screen by pressing the PrtScn (PrintScreen) key, though you'll have to paste the image into an app afterwards (like Microsoft Paint, where it can then be saved out as an image file, or Word, where it will appear in your document).
Press Alt+PrtScn together to take a screenshot of an active window or a smaller section of the screen that is in the foreground. Because there is no easy way to take a screenshot of a selected area that isn't the full screen (i.e. half an active window), the Snipping tool is your best bet.
To get to this, type ‘snipping' into the Cortana/search box next to the Start button, and it will appear. Click the arrow next to ‘New' in the tools menu to choose between a rectangular snip and a free form snip, which allows you to draw a line around any region of the screen to capture it. The image can then be saved for posterity using the File menu.
However, if you've installed the Windows 10 October 2018 Update, the Snipping Tool is no longer available. Snip & Sketch, which you can set to open when you hit the Print Screen key, has taken its place.