A clear screenshot can help explain an error to support or demonstrate a step in a guide.
Capture the right area
Press Windows key + Shift + S to open the capture overlay. Choose the area or window you need. Open the resulting notification to review and save the image, or paste it into a document.
Show enough context
Include the app name and exact error message when asking for help. Note what you did just before the error and whether it happens every time. A cropped image without context may make diagnosis harder.
Inspect before sharing
Look for account names, email addresses, customer details and notifications. Remove sensitive information in an editor and inspect the saved file before attaching it to a ticket or posting it publicly.
Further reading: Microsoft Support: Snipping Tool.