Trying to wrap my head around PHP password salt/encryption
$res = mysql_query("SELECT * FROM `users` WHERE `username` = '".$username."' AND `password` = '".$password."'");
                    $num = mysql_num_rows($res);
                    //check if there was not a match
                    if($num == 0){
                        //if not display error message
                        echo "<center>The <b>Password</b> you supplied does not match the one for that username!</center>";

$username = mysql_real_escape_string($_POST['username']);
$password = mysql_real_escape_string($_POST['pass']);
$pass_hash = md5($SALT.$password);
mysql_query(*query to insert $username and $pass_hash into db*)

$username = mysql_real_escape_string($_POST['username']);
$password = mysql_real_escape_string($_POST['pass']);
$res = mysql_query(*query to extract $pass_hash from db where username==$username)
//get the password from the $res and put it in a var
if(md5($SALT.$pass_hash_from_db) == $password){*correct pass*} else {*invalid login*}

// you save this in the database
$encPass = encFunction( $password.$salt );