These multiple combined symbols (Yantra) specialise in healing any ailments with the feet and your grounding (i.e. spiritual grounding and physical conditions such as: fungal infections, sprains and more serious ailments). However these symbols/yantras are much more that treating ailments with the feet. They are symbols that actually ground the individual to this plane - makes them one with the earth and creates an unbreakable bond between humans and the Universal OM.
The bonding symbols ground you and allow the recipient to take on-board other healings. Think of it as the root of the tree where other symbolic healings can built up from. The foundations of your being must be strong for the life vitality to thrive.
The healing symbols were said to have originated by Guru King Advaiyyan, but other Aaiyyanists say that the symbols originated from other Gurus/Saints. You may read other Aaiyyanist texts that say that these healing symbols originated from the 3rd Guru. Whatever the history - these symbols have been used for several thousand years and have been proved effective over the ages.
One of the most effective ways in using these symbols is to slowly trace the symbols on the sole of both feet using your index finger. If you or your client do not wish physical contact you can also trace just above the sole. While you trace the symbols, visualise the transfer of resonant energy and feel the power of the Loka opening and being brought closer to this plane.
Note: a more in-depth discussion on the healing Loka Yantras can be found in the official Hindu Aaiyyanist Healer's manual. This can be found here and is free to use. Do make sure you download it and use it to heal yourself and others and learn more about the Aaiyyanist path.