I was curious once so i acquired the sadhana from http://shop.fpmt.org/Cha-Sum-The-Ritual ... p_995.html
note: i have received no transmission or empowerment for this practice. however, it states under the link that it does not require empowerment.
After reading it, its way above my level. i believe asking a qualified person to
perform for you would be better.
directly quoting from the sadhana
"This ritual is said to be very powerful to eliminate obstacles which
occur in one’s life and spiritual practi ce. It is oft en performed by
lamas for the sake of one who is sick, when the illness is thought
to be caused by a class of spirits. This ritual follows the injuncti
ons of the Buddha, who taught that one should not harm any
living being, even those who do harm to oneself, and therefore,
rather than using wrathful means to harm the interfering spirits,
one off ers them tormas, praises, and various off erings such as
water, fl owers, incense, lights, perfume, food, and music."
However to sum it up, cha sum means three part. so cha sum puja = three part puja.
part one: offering to the worldly protectors of the ten directions
part two: offering to the interfering spirits known as don
part three:offering to the interfering spirits know as geg