how do I execute "node server.js" in codelab?

I am studying tutorial of codelab at https://bitbucket.org/webrtc/codelab/src/50a47bb092483fd7ca27998a365dff434919bf89?at=master

I've never used node.js before and wondering what this means under the "Running The Examples" section. I've installed node.js and installed which was straightforward but when I type:

node server.js

and I get

node: Command not found.

I am at below directory.and under that step6 directory, there is server.js exist.

xxxx@xxxx:/Users/xxxx/webrtc-codelab-50a47bb09248/complete/step6>

could anyone help with how node.js works?

Below is what i get when i type /usr/local/bin/node server.js under the same directory..

module.js:340
throw err;
      ^
Error: Cannot find module 'node-static'

at Function.Module._resolveFilename (module.js:338:15)
at Function.Module._load (module.js:280:25)
at Module.require (module.js:364:17)
at require (module.js:380:17)
at Object.<anonymous> (/Users/danielle/webrtc-codelab-50a47bb09248/complete/step6/server.js:1:76)
at Module._compile (module.js:456:26)
at Object.Module._extensions..js (module.js:474:10)
at Module.load (module.js:356:32)
at Function.Module._load (module.js:312:12)
at Function.Module.runMain (module.js:497:10)

This is what I got when I did npm install -g node-static

npm ERR! Error: EACCES, mkdir '/usr/local/lib/node_modules/node-static'
npm ERR!  { [Error: EACCES, mkdir '/usr/local/lib/node_modules/node-static']
npm ERR!   errno: 3,
npm ERR!   code: 'EACCES',
npm ERR!   path: '/usr/local/lib/node_modules/node-static',
npm ERR!   fstream_type: 'Directory',
npm ERR!   fstream_path: '/usr/local/lib/node_modules/node-static',
npm ERR!   fstream_class: 'DirWriter',
npm ERR!   fstream_stack: 
npm ERR!    [ '/usr/local/lib/node_modules/npm/node_modules/fstream/lib/dir-writer.js:36:23',
npm ERR!      '/usr/local/lib/node_modules/npm/node_modules/mkdirp/index.js:37:53',
npm ERR!      'Object.oncomplete (fs.js:107:15)' ] }
npm ERR! 
npm ERR! Please try running this command again as root/Administrator.

npm ERR! System Darwin 13.3.0
npm ERR! command "node" "/usr/local/bin/npm" "install" "-g" "node-static"
npm ERR! cwd /Users/danielle
npm ERR! node -v v0.10.29
npm ERR! npm -v 1.4.14
npm ERR! path /usr/local/lib/node_modules/node-static
npm ERR! fstream_path /usr/local/lib/node_modules/node-static
npm ERR! fstream_type Directory
npm ERR! fstream_class DirWriter
npm ERR! code EACCES
npm ERR! errno 3
npm ERR! stack Error: EACCES, mkdir '/usr/local/lib/node_modules/node-static'
npm ERR! fstream_stack /usr/local/lib/node_modules/npm/node_modules/fstream/lib/dir-writer.js:36:23
npm ERR! fstream_stack /usr/local/lib/node_modules/npm/node_modules/mkdirp/index.js:37:53
npm ERR! fstream_stack Object.oncomplete (fs.js:107:15)
npm ERR! 
npm ERR! Additional logging details can be found in:
npm ERR!     /Users/danielle/npm-debug.log
npm ERR! not ok code 0

When I type node server.js under the /usr/local/bin I got..

module.js:340
    throw err;
          ^
Error: Cannot find module '/usr/local/bin/server.js'
    at Function.Module._resolveFilename (module.js:338:15)
    at Function.Module._load (module.js:280:25)
    at Function.Module.runMain (module.js:497:10)
    at startup (node.js:119:16)
    at node.js:906:3