It's hard to peg Chaos Magic down to anyone belief. Since most of the time it tends to be tailored to individuals than to a mass practice. Chaos Magic can be a mass practice, but since it is not a openly practiced it cannot be gauged if people would be able to hold enough similar belief and will to actually achieve this. 

It does not help that the overall governments of the world do not recognize or if they do recognize Chaos magic they consider it a dark magic. Most Chaos users are solitary begins so they tend to shy away from studies of their magic or other magic users. 

Since magic is a practice there are some things like rituals, spells and meditation techniques that will allow you to tap into you will and express your beliefs.  Since beliefs are the actual bases of our powers as Chaos magic we must have stable beliefs and a strong will to back them up.  All magic is based obviously in rituals and spells more than the concept of meditation.  Meditation can be used to help with you Occlumency (guarding ones mind)  and Legilimency (intruding in another mind), these are actually easier to Chaos users than others. This is because of a Chaos users use of will is different from the normal magic. 

Only the belief in magic is a requirement to learn Chaos magic and of course magical ability, non-magical can learn certain aspects of magic, but it's not clear how much they able to understand seeing as most think that magic is not real. Even those who learn of real magic tend not to be able to believe in certain aspects of magic.  The concepts of Non-magical uses will be touched more in Advanced Chaos uses.  

This magic uses the concept that everyone must believe in something.  Any religion is usable in this concept so the gods you worship or that you make a contract with can help you with magical abilities.  You must remember though if your resolve, belief and will are weak so will your magic.