The simplest way to share files is to just create a dedicated shared folder on both PC's. Create a folder anywhere you want (C:/Share is what I use). Right click the new folder, and hit 'Sharing and Security', on the new screen, tick the box labeled "Share this Folder on the Network", then tick "Allow Network users to Change my Files" (also say yes to anything that might pop up wanting you to confirm the sharing).
One you've done that, hit OK and you should now have your share. On the other system, you can either look in My Network Places and hope it automatically shows up (sometimes refuses to happen), or manually browse to it by typing in '\\pcname\Share' (pcname = name of the system the share folder is on), if everything is dandy, you should open straight to that share folder.
You can also Map a connection to the Shared folder through My Computer in the Tools menu, if you really want (shows the share as a Drive in My Computer).
Probably not the best guide, but good luck!