Good question as it is not common knowledge in the Western world. Mala is a Sanskrit word meaning garland. It is a meditation aid to focus your mind during meditation and/or chanting. Traditionally there are 108 beads for the mala or any length divisible by 9 plus a guru bead. The guru bead should not be counted or touched by the thumb and is used as a starting and ending point of the recitation.
Malas have been used for thousands of years in Buddhism and Hinduism as a meditation aid however you do not have to be affiliated with any religion to wear or use a mala. Japa mala was adopted into other languages as the use and popularity of prayer beads spread. When the Romans invaded India, they mistook japa for jap, the Latin word for rose. Upon returning to Rome, mala beads were referred to as rosarium and later became known as rosary beads in English.
HOW TO USE A MALA
Hold the first bead between the thumb and middle finger and count with the middle finger and never the index finger. In Vedic tradition, each bead is held between the thumb (represents earth) and middle finger (represents sky), never use the index finger to count since it is the finger of fire and will burn your intentions. As you state your intention at each bead you are charging it with your energy and thoughts.
Always keep your mala in a pouch for protection and to show respect. When not in use, store in a special, clean and preferably sacred space.
HOW TO EMPOWER A MALA
To empower the mala and the mantra used, meditation should be practiced each day for 40 continuous days. When the mala becomes empowered it can be worn or lightly placed on oneself or others to transmit the energy of the mantra as well as the energetic qualities of the mala. When you use a new mantra with a mala, this energy becomes replaced, so it is recommended to use a new mala with each mantra if possible.