In Minecraft, when you register an account and buy the game, your player will be given a unique UUID that is associated with only your account. Your UUID can be useful for adding more complex configurations to your server such as creating a whitelist file.
1. Head over to namemc.com
2. Enter your username in the search bar and click search.
3. Click on your username
4. Here, you can view your current skin, history of names and most importantly, your UUID.