Help with Pre-populating form PHP

Using information that a user has already provided in their registration (and which is now in an SQL database), when the user signs in and then clicks to go to a form, I want some of the form to already be pre-populated. The log-in form is as such:

    <?php
    session_start();
    // check for required fields from the form
    if ((!isset($_POST['email'])) || (!isset($_POST['password']))) {
	header("Location: userlogin.html");
	exit;
    }
    //connect to server and select database
    $mysqli = mysqli_connect("localhost", "user", "password", "database")
			or die(mysqli_error());
     // use mysqli_real_escape_string to clean the input

    $email = mysqli_real_escape_string($mysqli, $_POST['email']);
    $password = mysqli_real_escape_string($mysqli, $_POST['password']);

    // Create and issue the query
    $sql = "SELECT username FROM frmak_form_1 WHERE
        email = '".$email."' AND
        password = '".$password."'";

    $result = mysqli_query($mysqli, $sql) or die(mysqli_error($mysqli));

    //get the number of rows in the result set; should be 1 if a match.
    if (mysqli_num_rows($result) == 1 ) {
	// if authorized, get value of username
	while ($info = mysqli_fetch_array($result)) {
		$username = stripslashes($info['username']);
	}


     $_SESSION['user']= $info['username'];
     $_SESSION['login_until'] = time() + 60 * 60; // login expires in 1 hour

     $display_block = "<p>Welcome, ".$username."!</p>
     <br /> <br />
     <a href='submitReview.php'>Click Here to Submit a Review!</a>";
     }
     else {
	header("Location: userlogin.html");
	exit;
    }
    mysqli_close($mysqli);
    ?>
    <!DOCTYPE html>
    <html>
	<head>
		<title>User Login REDIRECT!!!</title>
	</head>

	<body>
		<?php echo $display_block; ?>
	</body>

    </html>


Then the "submitReview.php" file is:

    <?php
     session_start();
     $s = &$_SESSION;    // Login status is ON and has NOT yet expired

     $isLoggedIn = isset($s['login_until']) && $s['login_until'] > time();
     if($isLoggedIn):
     $username = $s['user'];

     $s['login_until'] = time() + 60 * 60;    // extend login expiration to an hour from now.

      else
      unset($s['login_until'], $['user']);
      $username = null;

      endif;
      exit;
      }
      ?>

     <!DOCTYPE html>
     <html>
     <head>
     </head>
     <body>
      <p>
     <label>username</label>
     <br />
     <input name="usrnm" id="usrnm" type="text" value="<?php echo $username; ?>"/>
     <br />

     </p>
     </form>
     </body>
     </html>

In the example above, I'm only trying to display the user name in the form, because that's the only part that I want pre-populated as just a text field. The others are a radio button and a check box field, and I know those will take an even more complicated argument, so I'm just trying to make the simplest one work first.

If what I've done is not even remotely what should be done, could someone please just direct me toward a good tutorial for such things? I'm trying to teach myself PHP and MySQL, so sometimes it is a bit overwhelming. Thanks!