While many people like to use the words kink and fetish interchangeably, they actually have different meanings. The best way to differentiate between a kink and a fetish is by imagining a Venn diagram with kinks on one side and fetishes on the other and, in the middle, the similarities. While there is some overlap involved, kinks and fetishes have some key differences.
A fetish is about sexual objectification wherein an inanimate object or piece of clothing elicits sexual arousal . If someone becomes aroused by stockings, then the stockings would be considered a fetish because they are an object which elicits sexual arousal in the individual. Another example of a fetish is called Partialism. Partialism is a type of fetish where sexual arousal occurs from observing or touching a specific body part such as feet, hair, naval, hands, and ears  while a kink is focused more on the sexual behaviour itself . For example, engaging in degradation play, a consensual activity used to embarrass, demean, and humiliate the submissive partner would be considered a kink because it is considered non-normative sexual behaviour by societal standards. Other examples of kinks include bondage, voyeurism, and swinging, among other things.
One of the major theoretical perspectives as to how kinks and fetishes form is through Classical Conditioning . This learning process involves the use of an unconditioned stimulus (UCS), which automatically triggers an involuntary response in the individual . An example of this is cutting up an onion which causes the eyes to water. In this case, the onion is the unconditioned stimulus. Another example is if someone blows air into an individual’s eye, the individual will blink in response. The air is the unconditioned stimulus, which triggers an automatic response (the blinking). As previously stated, this kind of response happens automatically; it does not need to be learned.
In order for Classical Conditioning to take place, an unconditioned stimulus needs to be paired with a neutral stimulus in order to create a conditioned response (CR). At first, a neutral stimulus will elicit no response. However, if it is continually paired with an unconditioned response, it will start triggering the same response as the UCS. For example, opening a pantry door may initially be a neutral stimulus. If opening the pantry door is repeatedly paired with a dog receiving a treat however, the sound of the pantry opening will elicit a change in the dog’s behaviour and the dog may react as if they are getting a treat every time they hear the pantry door being opened. Thus, by pairing the unconditioned stimulus with a neutral stimulus many times, the dog has learned a conditioned response (expecting a treat and salivating in anticipation)
How does Classical Conditioning explain how Kinks and Fetishes form?
The kink or fetish can be reinforced by the individual becoming aroused or by orgasming in the presence of the object or activity. If an orgasm occurs while the individual is looking stockings, they will associate the stockings with pleasure and, when they masturbate again, they will want to observe the stockings because of the association to pleasure that it brings. In the case of those with this stocking fetish or a kink such as degradation, a classical conditioning approach would suggest that the interests were reinforced by masturbating (and then orgasming) to the thought of, or being in the presence of, stockings, or imagining one’s self being degraded. This theory has also been supported through research, such as in one study  where a group of heterosexual males were repeatedly shown images of boots (a non-arousing stimulus) and then immediately followed it up by showing them images of naked females (an arousing stimulus). After repeatedly showing images of boots followed by the nude pictures, the men eventually started showing signs of arousal to the boots alone by use of a penile plethysmograph, a tool that measures how sexually aroused a person is by how much blood flow is directed to the penis. A more recent study  was able to replicate this effect but instead of boots, the researchers used an image featuring a jar of pennies.
While there are many theories that look at how kinks and fetishes form, a classical conditioning approach offers a simple, intuitive explanation through pairing of a biological response and a neutral stimulus, suggesting that kinks and fetishes possibly develop due to an underlying process.
 Fichner-Rathus L., McKay A., Rathus, S., Nevid, J. (2016). Human sexuality in a world of diversity (pp. 408, 421). Toronto: Pearson Canada.
 Edlin, G., & Golanty, E. (2012). Human Sexuality: The Basics (p. 6). Sudbury, MA: Jones & Bartlett Learning.
 Chirinos, P., & Shahbaz, C. (2016). Becoming a Kink Aware Therapist (p. 5). New York, NY: Taylor & Francis Ltd.
 Mahabadi, N., Rehman, C., & Rehman, I. (2019). Classical Conditioning. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK470326/.
 Rachman, S. (1966). Sexual fetishism: An experimental analogue. Psychological Record, 16, 293-296.
 Plaud J. J., & Martini, J. R. (1999). The respondent conditioning of male sexual arousal. Behavior Modification, 23, 254-268. doi: 10.1177/0145445599232004