Nicola Tesla said if you wish to understand the Universe, then think of Energy, Frequency and Vibrating. Everything has a vibrating frequency, which is called resonant frequency.
How does it work? The theory, in plain English, can be explained using an analogy of an opera singer who uses her voice to shatter a crystal glass. The glass is vibrating at a certain frequency and when the opera singer sings at that particular frequency the glass shatters.
In the same way, each microorganism (fungi, bacteria, virus, parasite, amoeba, mold, etc) has a unique and specific frequency (or vibrational rate). When you add MORE OF THIS SAME frequency to the microorganism, it cannot tolerate it and it bursts or dies. Rife resonators generate resonance waves that destroy harmful bacteria without doing any harm to the users.