Yantras are sacred geometric diagrams that are used in tantric practice. They could be seen as the visual equivalent of Mantras. They are used in rituals and also just as objects of meditation and contemplation. Different deities or powers will have different Yantras and every Yantra will have distinguishing features. However, there are some basic components of all Yantras that can be identified and understood.
Generally, Yantras can be understood as maps of the progression from subtle unmanifest essence into concrete manifest reality. The center of the Yantra represents the unmanifest and the very outside is the final culmination into manifestation. Yantras may be worked with by starting from the center and proceeding out, mirroring the process of creation, or they may be worked with by starting on the outside and working inward, tracing a path of return to source through dissolution.
At the center of the Yantra, there is a dot that represents the unmanifest essence that is called the Bindu. It is analogous to the pure puruṣa/prakṛti “avyakta” principle of Sāṃkhya.
Outside of the Bindu, there are interlocking triangles or occasionally other pointed shapes that represent the creative forces. They are the underlying laws that allow for manifestation to take place. They are analogous to the buddhi or mahat level of the Sāṃkhya cosmology. Generally, upward pointing triangles are considered “masculine.” They orient energy from the individual into the Cosmic. They can thus be seen as dissolving. The downward pointing triangles are “feminine” and they orient energy from the Cosmic down into the individual. They are creating. The exact interplay between the two will depend on the individual Yantra. Some Yantras emphasize the masculine component and some the feminine and these components might overlap and interact differently depending on the arrangement.
Outside of the triangles will be a circle, which represents a unity or the infinity of possibilities that exist in this still potential form.
Petals emanate from the circle out in all directions and these are the first manifestations of subtle reality. They are often identified with the senses and other subtle elements of mind. So, this connects to the lower aspects of the Antaḥ Kāraṇa and to the Tanmātras. Depending on the individual Yantra, the number or exact arrangement of petals might vary.
Finally, the outside square of the Yantra is called the Bhūpura. It connects to the elements, the Bhūtas, and our final concrete manifest reality. The cardinal directions, which place us on this Earth are located in the four gates that are on each side of the Bhūpura. These are the access points to enter into the Yantra.