Not sure if it varies in each tradition, Kagyu wise anyway. It is a guru yoga that brings up the winds, channels, and drops and mahamudra, which generally in the traditional approach of most kagyu schools you would need empowerments to be practicing these types of activities. There are references to the purity of the skandas and seeing the body elements as dakinis etc... a tsog at the end and all that jazz.
So if not a required to practice, unless one has had previous exposure to all the theory and terminology it is going to be hard to follow. Personally I received an empowerment before I was introduced to the practice but not sure if it is the across the board standard.
Hope that is a bit of useful information.