What it means
The Sacral center is the body's main motor for life force and work. When it is defined and the Solar Plexus is not, it becomes the inner authority. It doesn't think. It responds. Asked a question, the Sacral answers right away with a pull toward or away from the thing, which many people hear as an "uh-huh" or an "un-uh". That response is the decision. The mind can find reasons afterwards, but it isn't supposed to overrule the gut.
How to use it
Get people you trust to ask you yes or no questions, and listen to the sound you make before your mind steps in. Open questions ("what do you want to do?") give the Sacral nothing to answer. Something like "do you want to take this job?" works better. If there's no response at all, that is information too.
Who has it
Only Generators and Manifesting Generators can have Sacral authority, and only when the Solar Plexus is undefined. A Generator with a defined Solar Plexus has Emotional authority instead.
Common mistakes
Asking open questions instead of yes or no ones, overriding a clear gut no with good reasons, saying yes out of guilt, and treating the mind's plan as a response.
How Cosmic Array reads it
Your authority depends on which centers are defined in your bodygraph. Cosmic Array works that out from the positions of 13 bodies at your birth and again about three months before it, calculated with the Swiss Ephemeris, and shows your authority next to your type, strategy and profile in the Architect blueprint. The Moon moves fast, so a birth time helps. Without one, the blueprint uses noon and marks the result as approximate.