are the computers networked? either by a fixed ip or a router of some kind?

it's actually very simple, go to system preferences/Sharing (by default the third group) on the left is a checkbox, where you need to select File Sharing ... you will get a 2panel view, on the left you can add folders you want to share, on the right permissions for those folders (add with the + icon)

setup sharing on both computers this way and then you will see the computers in Finder on the left below Devices