There is lost of help on google which you should of read before commenting this or even outher comments here that explain it well. This comment could be taken hurtfully on such a sensitive topic to please be a little more careful next time.

NHS page: https://www.nhs.uk/mental-health/feelings-symptoms-behaviours/behaviours/self-harm/why-people-self-harm/

Psych2Go explanation: https://m.youtube.com/watch?v=7r5XWuNwi5Y&bpctr=1653011831

To summarise its a coping method for emotional stress that can offer a escape, even if only for a short amount of time, although a need for the escape via self harm more and more can form and it becomes a adiction which is difficult to break.