PHP Basic : Adding form elements to MySQL

Create form :

<form name="addPerson" action="addPerson.php" method="post">
  <div>First Name:</div>
  <div><input type="text" name="firstName" size="40" maxlength="255" /></div>

  <div>Last Name:</div>
  <div><input type="text" name="lastName" size="40" maxlength="255" /></div>

  <div>Email Address:</div>
  <div><input type="text" name="email" size="40" maxlength="255" /></div>

  <div>Phone Number:</div>
  <div><input type="text" name="phone" size="40" maxlength="255" /></div>

  <div><input type="submit" value="Add Person" /></div>
</form>


Get and View Information :

<?php
   //get the form items.
  $firstName = addslashes(htmlspecialchars($_POST['firstName']));
  $lastName = addslashes(htmlspecialchars($_POST['lastName']));
  $email = addslashes(htmlspecialchars($_POST['email']));
  $phoneNum = addslashes(htmlspecialchars($_POST['phone']));

  //this will be for the error message to display
  //if they didn't fill out the form completely.
  $errorMessage = "";

  if(empty($firstName)) $errorMessage .= "You didn't enter a First Name<br/>";
  if(empty($lastName)) $errorMessage .= "You didn't enter a Last Name<br/>";
  if(empty($email)) $errorMessage .= "You didn't enter an Email Address<br/>";
  if(empty($phoneNum)) $errorMessage .= "You didn't enter a Phone Number<br/>";

  //now we check to see if there was an error
  if(empty($errorMessage)) {
    //everything is alright and we can now add it to the DB

    //these variables are used for database connection
    $host = "localhost";
    $user = "db_user";
    $pass = "db_pass";
    $database = "db_name";

    //connect to the database.
    $db = mysql_connect($host, $user, $pass);
    mysql_select_db ($database);

    //set up the query to add the information.
    $query = "INSERT INTO 'people' ('firstName', 'lastName', 'email', `phone`)
       VALUES ('$firstName', '$lastName', '$email', '$phone');";
    $result = mysql_query($query) OR die(mysql_error());

    echo 'You have successfully added ' . $firstName . ' to the database!';
  } else {
    //something was wrong.
    echo $errorMessage;
  }
?>