I Just Want to Know How Numerology Works

Numerology provides techniques for determining what energies have an effect on which areas of a person's being and their living of life.

The question about what makes it true could be considered to be based on a false premise. The energies exist. They are neither true nor false, as those imply a judgement. They just exist. Perhaps the Numerology vs. Predetermination will help with understanding that.

The energy is interpreted by people, which could be more or less accurate. Interpretations depend on a person's understanding of the essence of the energy being interpreted and of the situation or personal aspect the interpretation is applied to.

How Numerology Works is a good article for a basic understanding of the how-it-works aspect (as opposed to the how-to-do-it aspect).