Think of your spine as a bunch of hollow cans with a donut in between each one (the cans are the vertebra and the donuts are discs that cushion the vertebra and make your back flexible.,
Your spinal cord runs up the spinal column inside the vertebra.
You have compressed (squished) the donuts/discs and it is pushing out from in between the vertebra and pinching your spinal cord.
I am not a doctor...I don't even play one on TV!