The project panel is the component next to your textarea. It trees your entire project so you can easily navigate your project.
You can grab complete projects, packages, files, and classes from the project panel and drop them onto certain icons. Once drop it will do the action that icon does. for example: You can grab a file and drop it onto the delete label at the bottom of the project panel. This will delete that file.
You can alsot see all the packages, files, classes and methods in your project by simply expanding the tree.