Starting the server

[digitaldavenyc]

I ran the npm installer, downloaded the github files, and ran the terminal command to start up the server ... I get an error that says "cannot find module express". Any thoughts on what the issue is?

w8102hjsatm:example dave$ node server.js

module.js:340
throw err;
^
Error: Cannot find module 'express'
at Function.Module._resolveFilename (module.js:338:15)
at Function.Module._load (module.js:280:25)
at Module.require (module.js:362:17)
at require (module.js:378:17)