Taking screenshots

In short: A screenshot is a photo of your screen. On Windows use Windows key + Shift + S, on a Mac Cmd + Shift + 4.

In more detail: Screenshots are useful to show error messages, make guides or record something. The picture lands in the clipboard or as a file.

In Depth

Windows: Win + Shift + S opens the snipping tool: drag an area, the image goes to the clipboard (paste with Ctrl + V).
Whole screen: The “PrtSc” key copies everything to the clipboard. Win + PrtSc saves a file to “Pictures → Screenshots”.
Mac: Cmd + Shift + 3 (whole screen), Cmd + Shift + 4 (area).
Smartphone: Usually power and volume-down at the same time.
Privacy: Before sharing, check whether passwords or private data are visible.