>> First, I'm french, so sorry for the strange sentences.<<
There are many strange things about the French. Everyone in the world realises this. You are excused.
Your question regarding Satanic Ritual is actually quite a common one for those first exploring Satanism.
There is no actual belief in devils and demons. It's symbolic and you should perhaps re-read the section on suspension of disbelief.
The Satanic Bible provides a basic symbolic methodology that most Satanists will endeavour to expand upon in accordance with their own personal inclinations.
You might find my essay, A Brief Musing On The Nature Of Satanic Ritual
, helpful: http://www.newstatesman.com/writers/umberto_ray
Our high priest once pointed out that there is no requirement in Satanism for anyone to practice magic. But by exploring it you might find something works for you.
It is not that we summon demons and then believe that they will run out into the world and do our bidding. But rather that the human will, focused through effective symbols, might just impress itself upon reality. Reading Carl Gustav Jung's Man And His Symbols
might help you better understand how Satanism's practicies along these lines are more in tune with human psychology than mysticism.