There are many different exercises you can use to reduce back pain caused by slipped disc temporarily or permanently and these will generally involve stretching the spine slightly or opening it up. As mentioned, this back pain is a result of a trapped nerve that occurs when the spinal column loses its usual padding. Thus, by stretching out the spine you can often take some of the pressure off of the nerve and alleviate the pain. An example is to arch your back while on all fours like a cat which can be very effective or rolling up into a small ball.
Other exercises will focus on straightening out your spine to help to rectify anything that might be in the wrong place. Hanging from a pull-up bar, or getting someone to gently pull on your legs can often help, as can lying on the floor with your legs up on a chair at a right angle.