BeatLeader has an account system to distinguish between the players. This page will help you to understand basic info about the account creation, website usage and all the limitations of every platform.
You will be automatically signed up using the Steam information on the first game launch with the mod installed.
To log in on the website, goto this page and click "Log in with steam"
You will be automatically signed up using the Oculus information on the first game launch with the mod installed.
Oculus ID will be used as your account id.
To be able to log in on the website.
You don't need to own the game on Steam to be able to use it. It's just for the website, but if you will start playing Beat Saber on this Steam account scores will be posted to the same account.
To log in on the website, goto this page and use your login and password generated when you signed up on quest.