Benchwork is something which needs to be constructed properly the first time around; there is little margain for error, since your entire railroad will rest its weight upon the structure you create. No matter what sort of benchwork you have chosen to build, rest assured that even an inexperienced non-carpenter can create something to marvel at if they remember to take things slow and measure twice and cut once.
Materials and tools
For lumber, use 2x4 or 2x3 wall studs if you plan to go table top. If you're looking at something more advanced such as open-grid or L-girder, use 1x4 or 1x3 pine or douglas fir. You can use nails on the studs, but screws are usually more secure and suitable. If you use the 1-by lumber, it is almost imperative that you use screws- and pre-drill your holes to avoid splits. Some modelers like to use carpenter's glue to seal joints, while you're at it. For tools, you'll need a pencil, screwdriver, hammer, drill and bits, framing square, tape measure and hand or power saw.
Table-top / Open grid
For the beginnner, I recommend using a simple frame beneath a sheet of plywood. That is, build the frame in an open-grid fashion and attach a piece of plywood on top to use as a railroading surface. If you are using a single sheet of plywood, then use either 2 by 4s or 2 by 3s. Here's how it works: