There are two behavior-conditioning styles: classical and operant conditioning.
Classical conditioning is basically a dog understanding a simple association. The most well-known illustration of this is “Pavlovian conditioning.” We all remember the story of Pavlov’s bell, salivation, food association. Basically Pavlov started ringing a bell before the dog was being fed. During classical conditioning, the dog learns that the bell leads to the smell of food, which leads to the dog salivating, because the dog then receives the food. After classical conditioning the dog responds to the bell by salivating, because he has learned to associate the sound with food. The dog is now anticipating food at the sound of the bell.
Operant conditioning is teaching a dog that this particular behavior, will have this particular consequence. This is something a dog must learn to do (sit and wait for food), as compared to something the dog would do naturally (like salivate for food). Sitting and waiting to be fed is not something a dog would do automatically, it is something they must learn to do. Because the dog does not receive the food when he does not sit, he learns that sitting and waiting to be fed will get him the food instead.