When your spine is perfectly aligned, important nerve signals are able to be transmitted without any interference, but when your spine is out of alignment, the nerve signals have trouble transmitting.
Let's use an analogy to clear things up.
One of my personal favorites is comparing your spine to a garden hose.
So, think of your spine as the hose and and the flowing water as the transmission of important nerve signals.
When you kink the hose, or throw your spine out of alignment, the water (aka nerve signals) has difficulty getting through.
The severity of the kink, or misalignment, can determine the severity of your pain and suffering as well as the total overall function of your autonomic nervous system.