The user creates an empty dimension under their control, which can then be filled with the contents of their desire, using the power of the Shinju to do so. While physically tethered and connected to the Demonic Statue of the Outer Path, Madara was able to cast this genjutsu using only a standard Sharingan. After doing so, Madara could manipulate the otherwise blank and white world to create anything he wanted, no matter how detailed.
To trap every living being in the world within this genjutsu, however, the Shinju’s Rinnegan must be reflected off of the moon's surface. In order to do this, with the exception of Kaguya who ate the Shinju's chakra fruit, one must first become its jinchūriki. The genjutsu can be cast using the eye that blooms at the top of the Shinju’s original form or the third eye which opens on the jinchūriki’s forehead.
Upon the technique’s activation, the light from the moon’s eye illuminates the entire planet, turning it bright as day and making it impossible to escape. All living things are bathed in its penetrating light and immediately placed under the genjutsu. This causes the Rinnegan to be reflected in their eyes as they are rendered immobile, though their cognitive abilities remain unimpaired. The user can then use the God: Nativity of a World of Trees technique to ensnare the targets, assimilating their life force with that of the Shinju. Once this is done, the person is locked in a permanent genjutsu, in which they experience a dream world based on their individual desires, yet will live forever due to the Shinju’s power. Those tethered to the Shinju will eventually be drained of everything they once were and reduced to a shell of their former selves, becoming White Zetsu, ideal soldiers for Kaguya.(via sasukes10lover)