"Mantras are typically repeated hundreds or even thousands of times. The mala is used so that one can focus on the meaning or sound of the mantra rather than counting its repetitions. One repetition is usually said for each bead while turning the thumb clockwise around each bead, though some traditions or practices may call for counterclockwise motion or specific finger usage. When arriving at the head bead, one turns the mala around and then goes back in the opposing direction. This makes using the mala easier as the beads will not be so tight on the string when you use them.

White Quartz Mala Beads 108

If more than 108 repetitions are to be done, then sometimes in Tibetan traditions grains of rice are counted out before the chanting begins and one grain is placed in a bowl for each 108 repetitions. Each time a full mala of repetitions has been completed, one grain of rice is removed from the bowl. Often, practitioners add extra counters to their malas, usually in strings of ten. These may be positioned differently depending on the tradition; for example some traditions place these strings after every 10th bead. This is an alternative way to keep track of large numbers, sometimes going into the hundreds of thousands, and even millions.

The 109th bead on a mala is called the sumeru, bindu, stupa, or guru bead. Counting should always begin with a bead next to the sumeru. In the Hindu, Vedic  tradition, if more than one mala of repetitions is to be done, one changes directions when reaching the sumeru rather than crossing it.

There are numerous explanations why there are 108 beads, with the number 108 bearing special religious significance in a number of Hindu and Buddhist traditions.

Hindu tradition holds that the correct way to use a mala is with the right hand, with the thumb flicking one bead to the next, and with the mala draped over the middle finger. The index finger represents ego, the greatest impediment to self-realization, so it is considered best avoided when chanting on a mala."

                 Quote from Wikipedia   @  http://en.wikipedia.org/wiki/Hindu_prayer_beads