*important to note that this is not meant to be medical advice or serve as a diagnostic. This page is created for my own hobby/amusement. While I have done research, I am still a random person on the internet, please do your own research and look at the experiences of many people.
OCD is split into two parts, the obsession and the compulsion.
Obsessions are formed due to intrusive thoughts, which are categorized as any unwanted thought that causes undue distress and harm. It is important to note that everybody experiences intrusive thoughts to some degree, however while most are able to casually discard these thoughts, the way people with OCD deal with them (in the form of compulsions) creates the disorder. It is important to note that intrusive thoughts can be of anything that causes distress to the person having them. In media, this is usually stereotyped as being germaphobic or very orderly. However, there are many types of intrusive thoughts, some of which are very graphic, violent, and/or bigoted. "Magical thinking" Common fears that emerge from these types of intrusive thoughts are hurting family, friends, children, and animals. It is important to note that intrusive thoughts are unwanted thoughts. They are founded upon the fear and distress of the individual. Nobody can truly "succumb" to their intrusive thoughts, as they are not "secret desires" or anything of that sort. To judge somebody on the contents of their intrusive thoughts is illogical and unfair. While intrusive thoughts can be upsetting to hear about, it is important to remember that they will always distress the person who experiences them the most.
Compulsions are actions taken in order to "deal" with intrusive thoughts. These actions can be either mental or physical. Physical actions are usually focused on as they are easier to see. This can include sorting things, tapping certain objects, moving things around to ensure they do not form a line pointing at a person, etc. Mental actions are just as severe, even if they are not as "visible." This can take the form of listing things mentally or reviewing things. Some compulsions can be a mixture of the two, such as repeatedly searching a topic up online. It is possible for somebody to experience purely mental compulsions, which is informally called "Pure O" OCD. While compulsions are created to combat intrusive thoughts, they do not help. Instead, they help enforce the fear intrusive thoughts cause. They are merely another part of the vicious loop that is OCD.
In order to combat intrusive thoughts, OCD-havers must learn to view them as neutral. Rather than obsessing over their intrusive thoughts, they must let them merely pass over when they happen. This can be very difficult, as the upsetting nature of intrusive thoughts can make them hard to ignore. Additionally, since the core fear of OCD is the intrusive thoughts being "true," just ignoring them often feels immoral, even without the upsetting and frightening component. Compulsions can often become habit as well, which present another challenge in stopping them. One way to help with this can be to expose oneself to the source of the upsetting thoughts. While a lot of people's first instincts are to distance themselves away from others when they experience intrusive thoughts, interacting with the source of the fear can help the person center themself and can affirm the idea that they do not "really" or "secretly" want to hurt people. Outside stimulation may offer a distraction from intrusive thoughts, which is another plus.
It is important to note that if you know somebody with OCD, this is not a sign for you to force them to confront their fears. This is something that is hard to work up to and can take a lot of time and effort on the person's part. While you should be supporting and encouraging, it is up to the person with OCD to take charge of their recovery. It is also important to note that an OCD-haver may not want recovery. While this may seem frustrating, it is ultimately not up to you to become a person's healthcarer.