What is operant conditoning and classical conditioning?

Classical conditioning is the type of conditioning
associated with Pavlov’s work with dogs.   It describes when a stimulus triggers an
involuntary response.  This stimulus, to which subjects reply without training is
referred to as the unconditioned stimulus (UCS).  The involuntary response is referred
to as the unconditioned response (UCR).  Stimuli that to which subjects respond only
after training are referred to as conditional stimuli (CS).  Subjects begin to associate
CS with the UCS.  Eventually the presentation of a CS becomes equivalent with the
presentation of an UCR, and produces a conditioned response (CR) that matches the
original UCR.

Operant conditioning forms an association
between a behavior and the consequence that follows.  Something that increases a
behavior is referred to as a reinforcer.   Reinforcement can be positive or negative,
although negative reinforcement is often misunderstood or referred to inappropriately. 
When something desirable is presented after a behavior is demonstrated and it leads to
an increase in that behavior it is referred to as positive reinforcement.  When
something unpleasant or undesirable is removed when a behavior is demonstrated and it
leads to an increase in that behavior it is referred to as negative reinforcement.  
Negative reinforcement is often confused with punishment, which refers to consequences
that decrease behaviors or lead to them being demonstrated less frequently.  Punishments
can also be positive (something undesirable being presented after a behavior is
demonstrated leading to a decrease in the behavior) or negative (something desirable
being removed after a behavior is demonstrated leading to a decrease in that
behavior).