To make things simpler:
You have a dog. He hears you ring a bell, you give him food, once he sees the food, he salivates.
Again, you ring a bell, you give him food, he salivates.
Again, you ring a bell, you give him food, he salivates.
You ring the bell, but no food, he salivates.
You ring the bell, but no food, he salivates.
You ring the bell, but no food, he salivates.
You ring the bell, but no food, he does not salivate.
Again, you ring a bell, you give him food, he salivates.
Again, you ring a bell, you give him food, he salivates.
You ring the bell, but no food, he salivates.
What this does is associate the sound of the bell to him salivating. But remember, when you are experimenting with a human you need to know when to give them the food, or else they will stop salivating after a certain number of attempts.