Modern scanners tend to come with free photocopy software. Just press a button on your PC, or on the scanner, and you'll get a copy on your printer of the document that's on the scanner.
However, the software suite that's supplied with modern scanners tends to be huge, and some people (myself included) prefer not to install it. All we need is the scanner driver, which is normally just a megabyte or 2. The rest of the suite, such as photocopying and PDF creation, which can amount to 100 MB or more, stays on the shelf.
If you're in this position, but you'd actually quite like to have a simple photpcopier app on your PC, then you need iCopy. It's small, at around 0.5 MB, and runs under all recent versions of Windows. Assuming you have a relatively modern USB scanner and printer, it will automatically recognise the devices and so there's nothing to configure. Just press the "copy" button that appears when you run the program, and everything happens automatically.
I've been using this app recently in my office and it seems to work really well. Be aware, though, that you'll need to install .NET Framework 3.5 if you don't already have it.
To try out iCopy for yourself, go to http://icopy.sourceforge.net.