very, very easy to get confused what all these terms mean, when to use the etc, etc, etc.
First...
The field of study that explores them is of course psychology and it's "sub field" is Applied Behavior Analysis. so if you truly want to know the science behind terms like Operant Conditioning, Classical Conditioning, Conditioned Emotional Response, DRI etc, that get used in dog train regardless if you realize it or not or even if you know the terms or not...that is the direction I would suggest studying.
if you are willing to invest in resources such as Paul Chances book,
https://www.amazon.com/Learning-Behavio ... e+behavior
you will get a very accessible introduction to the science behind what we do in dog training. try buying used though.
Two of the best resources I know of at this time to learn about Classical Conditioning come from Cathy Sdao, who is an ACAAB ( a VERY impressive certification
http://www.animalbehaviorsociety.org/we ... r-caab.php) and former marine mammal trainer.
https://www.tawzerdog.com/programs/does ... ing-a-bell
https://www.tawzerdog.com/programs/cujo-meets-pavlov
so there are some resources if you really want to dig into this.
Second...the short as possible version.
Counter Conditioning.
The short explanation is you are replacing an existing conditioned response to something. for example, dog is scared of other dogs and will display the fear behaviors even if a dog isn't visually around but the sound of leash/collar/tags jingling can be heard. the jingle sound predicts other dogs triggering the anticipation of the dog followed by the fear. same idea with just the sight...see other dog...because of history of bad experiences it triggers the fear and fight or flight responses. Door bells ringing or knocks at the door that trigger barking and or excitement are another example of conditioned emotional responses (aka CER).
we can change (counter condition) what those "triggers" (sight of dog, sound of jingle, knock/ring at the door) predict which changes the CER and thus change the dogs emotional response to them.
Classical Conditioning.
Classical Conditioning is about associating something that has no value or meaning with something that does. the all time best known example is Pavlov's dogs. the sound of the bell predicted the coming of food, which triggered automatic responses in the dogs...drooling. But we can use the same science to counter existing conditioning...hence again the term "counter conditioning". A common misconception is that clickers or markers are involved...they are NOT. if you are clicking/marking you are NOT using Classical Conditioning.
If we are using Classical Conditioning something "out there" MUST predict the food. If you are working with a dog who is fearful, the appearance of the other dog(s) is what makes the food happen. we can never truly KNOW if/when our dogs actually see/notice/become aware of the other dog, but we can make very educated guesses based on the fearful dogs observable behaviors. ears prick up and orientate to the other dog. dog turns and looks in the direction of other dog. Body goes stiff. weight shifts from neutral to forward on the front legs or backwards on the back legs. Tail goes up like a flag pole or gets super tucked. hair goes up on their neck and back. you might hear chuff or growls coming from the fearful dog. their paws might sweat, they might "hold" their breath. mouth becomes tight and closed etc, etc. there are lots of cues the fearful dog has become aware of the other dog.
When the fearful dog has become aware...we deliver food with in 1 second to 1.5 second. we don't worry if the fearful dog is looking at us, siting, standing, laying down, rolling over, doing spins etc. all we care is that fearful dog has shown signs of awareness of the other dog...THEN THE FOOD FLOWS. we even give the food if the fearful dog barks, growls, chuffs, lunges etc.
Why do we give food even if the dog barks, growls, chugs, lunges...because this entire exercise is about the OTHER DOG making the food happen. Classical Conditioning is about linking the appearance of scary to the flowing of SUPER YUMMY FOOD. There is more to this, but first lets talk about another concept.
Desensitization.
This is about exposing our fearful dogs to whatever scares them in as low intensity as possible, but yet for them to still show smallest amount of awareness of scary BUT NOT start barking, chuffing, growling, lunging etc. when this happens, we have made a mistake. we got too close or let scary get too close. we take this information and do better next time. the goal is for the dog to NOT have a fearful or anxiety based reaction yet still be aware of the scary thing...other dogs. it may look like "nothing" is happening...but in reality this is where the learning is actually happening.
there are two ways Classical Conditioning works.
1. in the case of dog fearful dogs... "scary" dog appears.... one thousand and one.... start reaching for for and delivering food so that from awareness to arrive of SUPER YUMMY food is about 1.5 second max. a little longer is ok but you want to average about 1.5. once past this point food can be as fast as you can deliver in the early stages and STOPS once scared dog can't see scary dog any more or has lost interest in scary dog. starts all over again with the next appearance of "scary dog"...one thousand and one...start reach for food... and so on.
2. scary dog and food happen at the same time.
those are the ONLY two ways it will work.
common mistakes are making the food dependent on something the scared dog does. delivering food out of order. not using super yummy attention getting food. not waiting for reasonable indications that scared dog is aware of scary dog. getting too close to scary so that fearful dog has a reaction. And being tooo stingy with the food.
The goal is to achieve a change in the conditioned emotional response of "oh crap MONSTERS..." to "yahooo, yippy I just saw a dog". A common indication is the scared dog sees the other dog and before you can deliver the food, scared dog turns and looks at you..."where is my super yummy steak my favorite human, there is a dog over there" and of course we give the food. there are other possible CERs, but this is a common one.
Operant Conditioning. this is where food is a consequence of something the dog being trained dose. dog sits, sit makes food happen. dog lays down, laying down makes food happen. clickers and marker are a popular method implement Operant Conditioning.
Operant Conditioning can be used to counter condition as well. but you approach it a bit different. One example is the fearful dog can't turn away from scary...so they stare and develop tunnel vision and get more and more worked up and they start blocking us out because the SCARY MONSTER IS COMING TO EAT THEM.. one possible approach is to train the scare dog to look at you on cue. so then when out on walks you see the other dog coming into "range" and you cue the scared dog to look at you. the scared dog KNOWS the other dog is out there. the can hear and/or smell the other dog. But in this case we care about the behavior of the scared dog and the consequence of looking in your direction rather than at the other dog is...SUPER YUMMY food. Scared dog's behavior makes the food happen in this case. NOW...pavlov is still tagging along...remember the scare dog know the other dog is out there...they hear/smell it...and the food becomes associated with the scary dog.
even with using Operant Conditioning, you still MUST be mindful of a safe distance. you still want to be working that desensitization. if your scared dog has a reaction...mistakes have happened.
an non fearful example is my neighbors dog, she has been conditioning her dog to see cat...look on the ground for food. i was walking her dog one day and spaced on this...saw the cat...and noticed dog was looking around on the ground then looked up at me kind of puzzled...couldn't get the food out quick enough. her dog saw cat...cat predicted food on the ground. in this case classical conditioning was riding along...this is actually training an alternate behavior to trying to eat the neighborhood cats...but it also demonstrates a CER "dude!...I saw cat...and started looking for food on the ground...where is the food you dumb hairless ape."
mistakes will happen. that is just part of life. the training will over come them provided getting it right far out weights the mistakes.
ok...before I move into novel territory.... better stop here and make sure you don't have any questions. it can take a while to wrap your head around this because of the overlap in the principles.
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and it was over. 
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