Double click My Computer, then double click on your C: Drive to see all of your folders. Right click on a folder you want to share, for example My Documents. Select Sharing... from the menu that comes up.
From the Sharing tab, select Shared As, and you can type a file name in the Share Name dialogue box.
Select an Access Type. Your choices are Read Only, Full, and Depends on Password. Read only means people on other computers will only be able to read files in the shared directory. They cannot edit them or save to the folder. Full means they can open, and change files in the folder, or create and save them there. Depends on Password allows you to specify a password that allows users Read Only Access, and a different password for Full Access. Your choice depends on how much security you want on your files.
I strongly recommend setting some password protection even if you feel you don't need it. Some viruses attack network shares that aren't password protected.
Once you select a password, you'll be asked to confirm it:
After confirming it, click Ok, and that's it!
Printer sharing is similar, except that you right click the Printer you want to share instead of the folder. You can get to your printers by going to Start, Settings, and clicking on Printers.