The word Mandala comes from the Sanscrit and means "Circle/Centre and also Essence". It represents the process by which the Cosmo was formed from its centre; real mandalas allow a sort of initiatic journey to grow inside, through an intricate symbolism.
In general, mandalas have the power to armonize our mental state and the energy of the environment we are in. The well-being derivced from observing these wonderful circles is an interesting and relaxing exercise.