I normally organize my project in multiple files. Now, for the first time I have created a project at code.google.com/hosting.
How to add files to the project?
The project has got directory structure and many files. I want them to be visible under trunk (like it is in other projects).
NOTE: I am novice in this area (I have no clue about what to do). I am searching for an UPLOAD button.
You need to have a source code management system to be able to do that. Google Code typically uses subversion. Either download the commandline version or a GUI wrapper like TortoiseSVN. Then, you can upload all your project files.