ob_start and ob_end_flush meaning dscribed

 we call session_start(); we will not actually use the session variables but you will need it as part of the user login system. Then, we call ob_start() to create an output buffer. Typically, when PHP generates the page, it is sent to the browser as it is generating. By using ob_start(), the page and headers aren't sent to the browser until they've loaded completely, or until we call ob_end_flush(). By buffering the page, we are able to redirect using PHP at any point on the page, instead of just at the top. After the headers are sent, our only redirect option is with JavaScript. An enterprising hacker could easily turn JavaScript off, and then see our unsecured page in all it's glory. This one line allows us to deny the user access at any point in the page if needed.

Lines 4-8 set up our variables. $hasDB is a boolean used to determine if we are connected. $server, $user, $pass, and $db are the connection arguments for the server. Line 9 connects to the server, while line 10 determines if the connection was successful. If it was, we select the database to use; if it wasn't, we display an error message using die().