The Celestis Configuration is a building structure used to access the Celestis.
When built, the bedrockel will turn into smaller, 8x8 blocks (much like mob heads) attached to the sides of the Selemit Crystal, which becomes an animated, pulsating rainbow crystal block.
Simply right-click the Selemit Crystal to be transported to the Celestis. Once the Configuration is used, a corresponding one will spawn in the Celestis. This is what the player spawns on.