The practical content of Human Design is a small set of instructions, and it is worth setting them out because they are what a reading actually delivers.
Manifestors, roughly a tenth of people on the system's own figures, are described as able to initiate; their strategy is to inform those affected before acting. Generators and Manifesting Generators, together the large majority, are described as having a defined sacral centre and sustainable working energy; their strategy is to respond to what life presents rather than to initiate. Projectors are described as guides who see others clearly but lack consistent self-generated energy; their strategy is to wait for invitation or recognition. Reflectors, rare, have no defined centres at all and are described as sampling the environment; their strategy is to wait a full lunar cycle before major decisions.
Authority is the second half. Depending on which centres are defined, a person is assigned a decision-making mechanism: emotional authority, in which nothing is decided in the moment and the person waits for clarity across an emotional wave; sacral, a gut response; splenic, a single instantaneous intuition; and several others. The instruction in every case is to make decisions through that channel rather than through the mind, which the system treats as unreliable for personal decisions and suited instead to reflection and communication.
Further layers include the Profile, a pair of numbers from one to six describing a life role; the Definition, describing how connected the defined centres are; and the channels and gates themselves, each carrying a description.
Practitioners describe the work as an experiment: the instruction is to live by strategy and authority for a period, usually said to be seven years, and observe the results. Framed that way the system asks to be tested by the individual rather than to be believed.