Please help me with the Installation KnpSnappyBundle Symfony 2.8 : i just need to install a bundle which help me to generate pdf's files, but, i dont know how to start to install, i dont understand the documentation, the KnpSnappyBundle's documentation says to install with composer  to make:

    {
    "require": {
        "knplabs/knp-snappy-bundle": "~1.4"
    }
}

but i dont know where put such code.
Nevertheless I am open to other bundle in which i can create pdfs files, and please explain me STEP BY STEP how to install it, i am a beginner in symfony. 

since now thank you very very very much
