I need help to create a Dockerfile

I am new in Docker. Even though I have done the tutorials provided in Docker site, I am still not very sure how should I create the Dockerfile.

Basically, I will be using Putty in Windows to do all my stuff. So, I am rather confused how things should be done. Should I create the Docker image of my git clone in local first before upload it up to AWS using Putty in Windows ?

My next question is that how can I create the Dockerfile to make sure that all my NamedWebApp goes into a directory say /jsbackend ? I am really stuck here so would appreciate some help here.

And also I am new in node.js, react.js, redux so I come to know this json.package which will contains all the projects dependencies. My question is do I still need to download it when I build the docker image or when the docker image is built, it will contain the package.json and things will run ?

Please help me out on this cos I am really lost.
Thanks.