Is it safe to delete "My First Project.rcproject" file in the "iMovie Projects" folder? I am totally new to "iMovie" so I would like to ask you if it's safe to delete "My First Project.rcproject" file in the "iMovie Projects" folder (as it appeared from nowhere, maybe it was result of opening "iMovie")?

Thank you in advance.
That is the default name of your first project. If you haven't done any work with it, you should be able to delete it.