He will need to set some folders on the PC for sharing.
Right click on the folder and select Sharing, then give the folder a share name.
All files and folders within this folder will then be available across the network.
Don't just set the whole of your C: drive to shared though, as this would mean other users would be able to mess around with your system files.
Also, if you are sharing files across a wireless network it's imperative that you enable security in your wireless settings. At least WEP, but preferably WPA encryption.