Why do we need to use package.json? [duplicate]

This question already has an answer here:

What are the main uses for the NPM package.json file? 1 answer

I am new in programming languages. I was trying to learn web socket with java script to this site, but i am not understanding something that why i need to use package.json. This is my package.json file code

`{
  "name": "module-name",
  "version": "10.3.1",
  "description": "An example module to illustrate the usage of a package.json",
  "author": "Your Name <you.name@example.org>",
  "contributors": [{
  "name": "Foo Bar",
  "email": "foo.bar@example.com"
}],
  "bin": {
  "module-name": "./bin/module-name"
},
  "scripts": {
    "test": "vows --spec --isolate",
    "start": "node index.js",
    "predeploy": "echo im about to deploy",
    "postdeploy": "echo ive deployed",
    "prepublish": "coffee --bare --compile --output lib/foo src/foo/*.coffee"
  },
  "main": "lib/foo.js",
  "repository": {
  "type": "git",
  "url": "https://github.com/nodejitsu/browsenpm.org"
},
  "bugs": {
  "url": "https://github.com/nodejitsu/browsenpm.org/issues"
},
  "keywords": [
  "nodejitsu",
  "example",
  "browsenpm"
],
  "dependencies": {
    "primus": "*",
    "async": "~0.8.0",
    "express": "4.2.x",
    "winston": "git://github.com/flatiron/winston#master",
    "bigpipe": "bigpipe/pagelet",
    "plates": "https://github.com/flatiron/plates/tarball/master"
  },
  "devDependencies": {
    "vows": "^0.7.0",
    "assume": "<1.0.0 || >=2.3.1 <2.4.5 || >=2.5.2 <3.0.0",
    "pre-commit": "*"
  },
  "preferGlobal": true,
  "private": true,
  "publishConfig": {
  "registry": "https://your-private-hosted-npm.registry.nodejitsu.com"
},
  "subdomain": "foobar",
  "analyze": true,
  "license": "MIT"
}`

but i am not understanding why i need to use it. I tried to find on google but can not find something useful. One more thing if i create package.json then why i need to write dependencies ? why need it ? Please explain in poor man language beacuse i am not so good in english .

You do not NEED package.json. However, you will most likely want it. As you make larger applications using node.js, you will find that using other people's code is the best solution vs. writing the same thing yourself.

npm has lots of packages that people want to use over and over again. package.json provides a simple way for people to keep track of packages they use in their application.