You can scan a document in using either a scanner attached to a PC, or to an inkjet printer attached to a PC (that also has scanner and copier capabilities)
It is usually as simple as:
laying the document you want scanned face down on the glass plate....
...and then either pressing the "scan" button on the scanner/printer, or opening up the software that came with it and selecting the "scan" option.
The document will scan and then be automatically copied to the computer hard disk.
Exactly where it puts it, and what it calls it, will differ depending on what scanner or printer you have, so you may need to hunt around in "My Documents" or your personal area on the hard disk.
You sometimes get a choice of what TYPE of file it creates, and it may create a BITMAP or a JPEG file or somethng else.
Once it is on your PC you can open it with Paint, or any other program used to open image files.