Do you have a network cable you can connect them with?
Link the two together, and on the PC, right click the folder you want to share, choose 'Sharing & Security' and tick the box which enables access from the network (can't remember exactly what it says).
Then on the Mac, open any Finder window, for example by clicking on the 'Finder' icon at the far left hand side of the dock. On the left hand side of the Window which pops up, you'll see an icon representing your PC, just under the 'shared' header...