Rituals are ceremonies performed by a group of Avatars to focus their will power and by this their dream energy on a common goal in order to shape the tissues of The Dream. The more focus is achieved, the stronger the effect will be. It is even possible to definitively alter the axioms of the Dream. Example of such powerful Rituals can be found in the Saga of the Dream.
However, some competences and some specifics places are required to conduct rituals. Not every Avatar is able to control and direct the huge focus energy of a group of Avatars. It is also possible to increase the focus of a ritual by "artificial" means.
Rituals are not necessarily religious or magic. Any type of focussing ceremony does the job. A ritual can be a religious sanctification, a dark sacrifice, a magic séance, a scientific experience or the construction of an invention. The important thing is to create a high level of dream energy bundled to one single will.
Consult also The Dream - Basic Principles.