Yesod
The sephirah of Yesod translates spiritual concepts into actions that unite us with God.
It is often associated with the Moon, because it is the sphere which reflects the light of all the other sephirot into Malkuth, and it is associated with the sexual organs, because it is here that the higher spheres connect to the earth.
It plays the role of collecting and balancing the different and opposing energies of Hod and Netzach, and also from Tiferet above it, storing and distributing it throughout the world. It is likened to the 'engine-room' of creation.
The archangel of this sphere is Gabriel, and the Cherubim is the Angelic order.
Read more about this topic: Yesod (Kabbalah)