How to recognise each user through SQLite DB?

I am new to Android and trying to understand how a user can be identified as his own data when he retrieves a List view of his for example To Do list.

At the moment I currently have 1. Register 2. Login, checks the database if username and pass equals to his input 3. Add a ToDo note onto the SQL? 4. Retrieve the ToDo note once added uniquely to him?

How can I do this? Currently I only have 1 table which are the users and will be making multiple tables.

Login

boolean loggedIn = false;
SharedPreferences pre;
static public Context context;

public void onClick(View v) {

    Controller handler = new Controller(getBaseContext());
    handler.open();

    if (username.equals("") || password.equals("")) {
        Toast.makeText(getApplicationContext(), "Please fill in all fields", Toast.LENGTH_SHORT).show();
        return;
    }
    if (handler.executeLog(username, password)) {
        Toast.makeText(this, "Successfully Logged In", Toast.LENGTH_LONG).show();
        Intent log = new Intent(this, MainActivity.class);
        pre.edit().putBoolean("LoggedIn",true).putString("username", username).putString("password", password).commit();
        startActivity(log);
        handler.close();
    } else {
        Toast.makeText(this, "Invalid Username/Password", Toast.LENGTH_SHORT).show();
    }

DBControl.java this is where all my rawQuery are executed.What methods do I add?