Buddhists who meditate are referred to as practitioners. Practice may include the saying of prayers and integrating Buddhist principles into all aspects of life such as diet and marriage.  Besides studying texts, chanting or saying prayers, there are other special activities associated with training the mind to benefit from the Teachings of Buddha.  This is especially true with regard to the tantric approach; Vajrayana is enhanced through the use of symbolic or ritual items and activities.

MANDALA is a tantric meditation device. It's a visual aid for concerntration and introvertive meditation leading to the attainment of insight and to activation of forces culminating in "siddhi" supernatural forces.The mandala is the graphic representation of this process. It is not only  theoritical but practical as an operational scheme involving a clear plan for practical realization of the process within one self.It thus becomes an instrument. There are so many types of mandala ,depending on the nature of the central deity. 

Dorje is the Tibetan word for vajra. Do-rje means noble stone. Do = stone and rJe = noble or prince. It embodies not only the brilliance of refracted or reflected illumination, but it also symbolizes the impervious and fixed solidity of the point of power around which all else turns - the axis mundi or hub of the world.   A dorje, then is like the diamond, but that precious stone is an inadequate symbol for it.  However, just as any other substance will be destroyed on impact with a diamond, so the ritual object symbolizes that which is indestructible, enduring, powerful, invincible, and irresistible.