For my best knowledge so far, the biggest difference between SQLite and MySQL is that it does not require a server to run, as SQLite stores data in a database file in each device.
The question rising from this part is..
Let's say I created an Android app which simply contains login and signup features. By installing this app in one device I create an ID with a password (let's say the ID is ricoangeloni and the password is 1234).
If I install the app in another device, is it still possible to log in with the pre-made ID? This is still very confusing, as I am probably not sure if the clients are sharing the centre database.
Best How To :
The answer to this question depends on where the database is located (regardless of whether you're using SQLite or MySQL to access the database). If you're storing the database on the Android device, then that database is specific to that device.
If the database however is stored on some internet-facing computer (doesn't have to be a "server" per say) and your app interacts with that hosted database, then an account created in that database is accessible from anywhere, not just your app. A website for example could also use the accounts in that database for login purposes.
The approach of housing the database on the device does have its advantages, namely you don't need to have a dedicated machine to host the database. But, if you wanted to have one database with all of the accounts and use that for authentication purposes, you're going to need to put that database on the internet.