Are you speaking of a SQLite database. If so:
1. Use inputText of the dialog library to enter a user name and a password. You can also use 2 edittext boxes instead.
2. Have a table in the database that stores all users and passwords in 2 different fields.
3. Go over all the records in the table via a cursor. When the match is found, the user will be allowed to continue. If not, a message will pop up. Subsequently, the database is closed and the activity is finished.
This is not a terribly secure method, but works. If this is what you want and If you need help with the code, post again. many of us are always willing to help.