Goto
php.net and read. What he posted would work just fine provided you have db.php and your database table is named address and has a
single field called address.
The form is displayed if it hasn't been submitted. It displays confirmation or error based on if address valid or not. Even with the include commented out, I see the form, can submit a non-valid address, and receive an error, with form now hidden, since it was posted.
If you're expecting someone to do all of your work for you and just copying and pasting code from various sources, your db.php include is probably broken too. I would recommend not directly inserting form variables into the database unless you like SQL injection. You should probably also modify what he provided to check whether the data was successfully inserted or not and display error/confirmation based on that. Right now it displays nothing (blank page) when submitting a valid address if the insert fails. That's probably where your confusion lies because you are not reading or understanding the code presented to you, however, it is a perfectly fine working example.
People aren't going to want to help you if you make no attempt to learn and are rude.