Office Guy was asking if you had set up for a local testing-server, but I'm not sure you answered! I don't know your situation, whether you have set up your computer with a testing server (i.e. Xampp, Mampp (mac) or IIS with php & Mysql) - or whether you will be testing your pages by uploading and viewing online. If you're not sure if you're viewing your files on a testing server or not, I'd guess that you haven't set one up on your machine yet.
You don't absolutely need one, but adjusting and previewing your files offline makes customising the look and feel and testing the functionality of your sites so much easier when you're working with dynamic pages. Check out the link Office Guy posted above - it'll be really useful for another time, even if you choose not to test locally now and just upload your files.
Whether you're testing your site locally (testing server) or uploading your files and viewing them online at your www.yourdomain.com site, you will have to have set up a database (as per instructions) - either one created for use by your machine's testing server, or one set up on your remote hosted server (usually accessible from your site control panel). In either case, you need to have edited your Connections/localhost.php file with the correct details: - localhost name (usually just 'localhost), database name, database user name, database user's password. Your pages look for this info when they load, so it needs to be there.