could someone explain how the vacuum system works? and what it does?

 

The vacuum system is for cleaning the carpets, etc.
(Just couldn't resist....sorry)

Vacuum is produced by the downward motion of the pistons while the intake valve is open. This vacuum is measurable and is often used to diagnose performance problems and engine condition.

Since it's available for 'free', many systems use vacuum to perform their functions. These can include fuel management, damper controls on the ventilation system, brake booster function, cruise control, evaporative emissions control, EGR, etc.