NPM

$npm install twilio

will install to

./node_modules

./node_modules/twilio:

package.json

name properties, info about the project
manage dependencies ("dependencies:{...}")
"devDependencies" - only in a development environment
"scripts" declare tasks ("scripts":{"test":"jasmine-node spec"} -> $ node test will run the jasmine tests (like Grunt)
"main" the path to the javascript file which is the main part of the library (e.g. /lib/index.js) : in /lib you can have an index.js which defines the public interfaces
"engines" which version of node to use

then you can use it

  var twilio = require("twilio");

var client = twilio();

client.sendMessage({
    to: "+1555555",
    from: "+15555555",
    body: "hello wold"
});

most modules use an async API (here in twilio a callback)

error-first

  client.sendMessage({},
    function(err,message){
        // advises to use this pattern 
        // when writing modules for NodeJS
    }
)

Abundancia