SharedPreferences sp = context.getSharedPreferences("loginSaved", Context.MODE_PRIVATE);
SharedPreferences.Editor editor = sp.edit();
editor.putString("username", "some user value");
editor.putString("password", "some password value");
editor.commit();

SharedPreferences sp = context.getSharedPreferences("loginSaved", Context.MODE_PRIVATE);
String username = sp.getString("username", null);
String password = sp.getString("password", null);
if(username != null && password != null){
    // login automatically with username and password
}
else{
    // login for the first time
}