Every time you create an account, submit a form, or do anything online, something somewhere is assigning you a unique ID. Most of the time, these are UUIDs - Universal Unique Identifiers.
Why Not Just Use Regular Numbers?
Regular sequential numbers have problems. What if two people sign up at the exact same millisecond? What if you need IDs that work across multiple databases? UUIDs solve all of this by being randomly generated and practically guaranteed to be unique.
I generate UUIDs constantly for testing, database work, and even just to have unique identifiers for anything I need to track.