The Ubuntu Tour gives you a quick overview on the look and feel of the Unity desktop in Ubuntu. It is in no way a full blown operating system but rather a nicely done interactive graphical depiction of the user interface.
To find out how Ubuntu operates in reality it is a much better idea to download the installation DVD .iso, put this on an USB drive, and then let your computer boot from this.
You will be presented a choice to "Try out Ubuntu" which will boot your computer into a fully operational live system, leaving your computer's hard drive untouched. Doing so is a great way to test your hardware for Ubuntu compatibility.
You could even install programs from the software center if you wished. It is not restricted in functionality in any way other than you will not have a HOME directory to store your data, and installed applications or application settings will be lost after a shutdown.
But you will find out that Nautilus does have a menu bar, now as with all other applications integrated in the top panel ("global menu"). In case you do not like this, you can easily disable it.