Android :: Database Connection - Check Data - Login Page?

I'm doing Major Project on my final year and I'm very new to Android plus I;m not good at codings. I need help with my login page. I've created something like a database connection java file which is this:

CODE:......................

I've already created a database for users using SQLite. The database name is Users and the table is called User. The records inside the table are Username, Password, LastName, FirstName. I've inserted one user's info into the database. The problem is I do not know whether my UserDB.java is correct.

And I've also created login.java. Hardcoded Login page:

CODE:........

So I want to know how I should apply the database connection on the login.java. Should I insert database connection something like db.Open();? I studied ASP.Net a few months back and I kind of forget most of what I've learnt.

So how should I open the database connection on login.java and how to check with database whether the user enters the right username and password?

Just incase you need my xml, here's the code:

CODE:......

I need to learn how to do it so that I can apply for other pages for example Register.java page.