Yantras are the maps of consciousness, geometric forms that were visualized by yogis in deep states of meditation when they tried to experience and understand the subtle vibrations within their own bodies and the cosmos.
When you look at a yantra, it makes a huge impression on the energy patterns of your mind.  These inner energy patterns begin to respond to concentration and awareness when you meditate on a yantra, as those images create powerful psychological impressions.
Concentration on yantras develops intuitive as well as creative ability.