Surrey County Council has a very good website covering the Greensand Way.
A delightful publication detailing the route, with lovely illustrations and fascinating background information, is: "Along and Around the Greensand Way: Guide Book, Route Guide and Footpath Maps Including Ordnance Survey Maps," written by Bea Cowan and illustrated by Matthew Cook. It is available from the usual outlets, online and otherwise. Although it is now some time since it was published, it is a treasure to own and indispensable, whether you are walking a specific section or the entire route. In the same series, there's a good 'un on the Saxon Shore Way but hey, this website is about Surrey.