I received this message when starting greenfoot on ubuntu 11.10

I'm a newbie and not sure where does the file located (greenfoot)

The project is read-only.How and where do I change the permission? You will not be able to create objects or execute methods. Either the access rights of the project directory are set as 'read only' for you, or the whole file system is not writable (is it a CD?).

To fully use this project, you must ensure that it is on a writable file system (usually your hard disk), and that you have write permission in the project directory and each file within it.

This can often be accomplished by choosing "save as" from the Project menu after closing this dialog.