Creating login/registration form with existing database

Hi. I'm new to android. I'm trying to create a login/registration form. I have already created the layouts. Also, i have create my database.sqlite using SQLite browser
http://sqlitebrowser.org/.
Basically, i want to create login form with the existing database. I have already code it and the database is connected to android studio with the help of this link
Http://developinginandroid.blogspot.sg/2014/01/connect-db-sqlite-to-android-with.html
My table name is call "User". Field name are email and password.
I have been searching and watching but none teaches on using existing database.
Does anyone have tutorial links for me regarding on how to use existing database to create login/registration. I just need the tutorial links.
Thanks