I think you are misunderstanding how a file field works.
A file field allows the user to select a file that exists on the client computer, not the server.
you cannot simply add a file field and have the file be uploaded to the server, you will need to add additional code to the page for the upload to occur.
The Universal Email extension includes an Upload file server behavior that can be used to transfer the file from the client computer to the server.
as for storing the file name in the database, yes, it will only store the name not the path.
the path will change from page to page depending where it is on the site. when creating the link, you should include the path to the file upload location.