On my laptop, with Windows 10, I simply press PrtSc on the keyboard, (there will be no acknowledgement that you have done this on screen), then minimise the document I am working on, open e.g. Blank Document and Paste.
Computer: Print Screen.
Laptop: Fn+ Prnt Scrn.
Mobile: Often, pressing the power and home buttons together, and holding for a few seconds, will do the trick.
For computers and laptops, the screenshot is temporarily held until you do something with it: most sensible thing would be to open Paint and Paste the image, then save it.
Phones save it directly to the image folder, and also open it for you.
Are you on a laptop keyboard? On mine and on my work PC (separate keyboard) it's Ctrl and Prnt Scrn buttons at the same time. Then you have to paste it somewhere - into a doc, an email or Paint as suggested with a name.
On my laptop, with Windows 10, I simply press PrtSc on the keyboard, (there will be no acknowledgement that you have done this on screen), then minimise the document I am working on, open e.g. Blank Document and Paste.
Thanks Murraymint! This is the first time I have ever answered on Technology, feel quite pleased with myself! Glad to be of help.
(I have however posted queries and have benefited from the advice given)