A general description of SAMBA is:
Software running on a *nix box that causes some *nix folder to appear on a windows network as if that folder is on a windows machine. Samba does this by having that folder, known as a share, speak NetBIOS. NetBIOS is the protocol (language) that windows networked folders (shares) speak to each other.
A very nice and free online book is:
http://www.oreilly.com/catalog/samba/chapter/book/