How do Yantra works
At the basis of yantra operation is something called "shape energy" or "form energy". The idea is that every shape emits a very specific frequency and energy pattern. Examples of old believes in shape energy are the yantras and mandalas of eastern philosophies, the star of David, the five pointed star (pentagon), the Christian cross, the pyramids and so on. Certain 'powers' are inscribed to the various shapes. Some have 'evil' or negative energies and some 'good' or positive energies, but in YANTRA Yoga, only the benefic and harmonious energies are used.
When one focuses on a yantra, his mind is automatically "tuned in" by RESONANCE into the specific form energy of that yantra. The process of RESONANCE is then maintained and amplified. The yantra acts only as a "tune in" mechanism or a doorway. The subtle energy does not come from the yantra itself, but from the MACROCOSM.
Basically, yantras are secret keys for establishing RESONANCE with the benefic energies of the MACROCOSM. Very often the yantras can put us in contact with extremely elevated energies and entities, being of invaluable help on the spiritual path.