How to store and organize data in a firebase realtime database with sequential number tags such as 1/001, 2/002 and so on?

Hi app experts, please help. I want to design an application on login using roles like admin, user. To authenticate I use firebase authenticated and for roles I want to use firebase realtime database. I have completed how to log in using Firebase authenticated but I am still confused about how to save the data of users who have registered and the roles selected in the real-time Firebase database by storing data with sequential number tags such as 1, 2, 3 and so on. which I will later use to log in to applications with different role features.

Firebase not accept space symbol emoji so use “your text” for store data

okay, thanks, that’s why I want to tag the user data using the sequence number 1, 2, 3 and so on, can you tell me how to do it using an example block?