Still confused about SQLite vs. MySQL

I am new to developing Android apps and I am deciding on whether to use SQLite or MySQL for my app.

I am still confused about what SQLite is and how it works. Please excuse my noob questions.

As far as I understand it, SQLite is local storage and serverless. My app will require user account registrations, so I'm not sure if that's possible with SQLite. I mean, how do you store user account information locally using SQLite? Say I have 3 users signing up, does each user only store THEIR username and password on their phone? So each user sees a different value for "username" and "password" in their local database? Since there is no centralized database, does that mean I as the developer do not have access to any of the users' information since all the information is stored locally on the users' phones as opposed to on a server? Why is SQLite even useful then?