Hello, what is the difference between a Primary Album and a normal Album? What is the difference between ticking PRIMARY ALBUM INSTALLATION or not for a new user? Best regards

The primary album is an album that is automatically created for the user so he has manage rights to it. You can further assign other albums to a user as well. Note this is currently only possible fro top level albums: http://www.zenphoto.org/news/an-overview-of-zenphoto-users