There are 7 energy centers, called "chakras", in your body. A happy and healthy body, mind and spirit essentially have their roots in the balance of chakras. These chakras are represented by the semi-precious stones with 7 colors: Purple, indigo, blue, green, yellow, orange and red.
Meanwhile, the "Om" word is considered the sound of the universe, the "seed" of all mantras. Om corresponds to your 7th chakra, connecting you to the Divine self. Chanting "Om" can help you relieve stress and improve focus.