The Dropzone is a plugin written by a different developer and has its homepage at http://www.dropzonejs.com/. You can read how to use the features Dropzone has to offer there.
First of all, the script file where you're writing the dropzone code needs to be included only in the page where you want the dropzone to appear.
The document ready function is necessary to tell the page: Start the script only once the document is ready to do so.
Here's a StackOverflow question regarding how to include multiple Dropzone instances on the same page: http://stackoverflow.com/questions/26657489/multiple-dropzone-in-a-single-page
Let me know if there's anything else you need help with.