I am working on Google drive application which will allow user to create file which must be public.
I could see some example where we can create a file
You can set the Access Control List of the file using the Permissions feed. The documentation is located here:
https://developers.google.com/drive/v2/reference/permissions
To make a file public you will need to assign the role reader to the type anyone
Then, if you want a link to share to people, you can grab the webContentLink URL returned in the File metadata in the API, it will allow any users to download the file. You can also use it to embed the shared file into HTML (for instance images in tags) .