Self-tutoring about Windows: the tutor mentions a necessity he’s had to discover.
To prove a program result, etc., a person might be asked for a screenshot.
Alt+PrtScrn takes a screenshot of the active window and puts it on the clipboard. You won’t necessarily know it’s done so, however, until you paste it into a file (in Paint, for instance).
Source:Oracle Tutoring by Jack and Diane, Campbell River, BC.