In the dailogue box that appears, enter the project file name and the folder in which to save the project file. Marionnet project file names have the “.mar” extension and they store the network topology information and the COW file systems for the UML virtual machines associated with each network element created in the project so node configurations are saved in the project file.
Once a project is created (or opened) you will be able to add routers and link to the GUI and start experimenting.