The mantra Om Mani Padme Hum (literally: "Aum, to the Jewel in the Lotus, hum) is recited by Tibetan Buddhists to invoke Chenrezi, the Bodhisattva of Compassion. Repeating this mantra accumulates merit and eases negative karma; meditating upon it is believed to purify the mind and body.
Spinning prayer wheels, physical or digital, are believed to confer the same benefit as speaking the mantra. It is often recited with the aid of a mala (string of prayer beads.)