"Yantra" is a diagram which comes from ancient Indian and Tibetan wisdom. Similar diagrams expressing the universal order are found in many cultures, including that of Europe.
Yantras are made to harmonize your inner space with the orderly energy.
They help to compensate disharmonic or negative energies in inner spaces
(like electric ionizers which improve inner environment by raising the negative ionts proportions).
Yantras are known to be used for meditation as well. Meditating on this diagram mind is being clear and calm.
According the traditions "Sri Yantra" (which means "Big Yantra") expresses the order of the cosmos through symbols. The original Sri Yantra diagram originates in the mutual transitions and harmonic arrangement of given building elements: "male" triangles with their peaks upwards, and "female" triangles with their peaks downwards. The diagram bonds together all the principles that our earthbound existence is built on.
They are a sort of a sacral pictures which traditionally support spirituality of temples.