Hi Mr Who,
Lead scoring is used to attribute points (a score) to a contact based on some activity they might do. For example, purchase a product = 10 points.
Point thresholds can then be used for automated marketing purposes. The best explanation would be in the Kentico documentation:
https://docs.xperience.io/on-line-marketing-features/managing-your-on-line-marketing-features/contact-management/scoring-contacts