Obsessive-compulsive disorder commonly referred to as OCD is a mental disorder which manifests itself as an insatiable and uncontrollable urge to have things be "just right." OCD often involves driving a person to repeatedly perform a certain action or series of actions in an effort to quell a feeling of anxiety caused by their OCD, which can also involve "rituals" or routines that are strictly adhered to for a similar purpose. OCD can also cause thoughts which can be heavily distracting and thoughts and impulses known as "compulsions."
These impulses are often highly impact-full and interrupting to daily life, and can be seen as crazy and impulsive to observers. The thing about OCD is that in many cases the person with it is aware what they are doing is nonsensical and they have no logical reason to continue their actions yet they are unable to stop themselves.
We have all seen the videos and pictures of hoarders which is a common manifestation of OCD, in which a person cannot bring themselves to part with an object for fear of wasting its value. There are an infinite number of compulsions and rituals that a person can busy themselves with so going in depth on the various cases and examples is rather fruitless, instead if one experiences anxiety by the state of things around them and an uncontrollable urge to fix it, they may have OCD and should seek the help of a mental health proffesionsal.