All PC keyboards have a key marked ‘Print Screen’. This may be abbreviated to say ‘PrtScn’, ‘PtSn’ etc.
Historically these would literally print out what was on the screen, however the modern usage is to capture the current screen and copy it as an image to the Windows clipboard. If you open an image editor, e.g. Paint, you can use Ctrl+V to paste it in.
To capture the current window only, e.g. the internet browser you are currently using, then hold down ‘Alt’ when pushing ‘Print Screen’