You are absolutely correct!

Everything to the left of the “@” sign is called the “username.” And it is chosen by you when you sign up for an email account.

And just so you know, everything to the RIGHT of the “@” sign is called the “domain name.” It is the name of the company that “runs” the email service being used.

Think about what your “user name” might be as you tap on your answer to this question: Are you ready to sign up for an email account?