PHP function not passing data to MySQL - php

Question

I've setup a sign up page to register users, its passed from HTML and into PHP
however the PHP function is not passing it over to the MySQL database
<?php
try{
$db = new PDO ("mysql:host=localhost;dbname=car_rental;port=3306","root","");
}
catch (Exception $e){
echo "SQL is Off";
exit;
}
echo "success";
try{
$trial = "INSERT INTO users (firstName) VALUES ('trial')";
}
catch (Exception $e){
echo "doesnt work..";
}
echo "works?";
try{
function NewUser()
{
$firstName = $_POST['firstName'];
$lastName = $_POST['lastName'];
$age = $_POST['age'];
$email = $_POST['email'];
$password = $_POST['pass'];
$query = "INSERT INTO users (firstName,lastName,age,email,pass) VALUES ('$firstName','$lastName','$age','$email','$password')";
echo"user created";
}
}
catch (PDOException $e)
{
echo "ERROR -_-";
}
?>
is this the correct implementation to execute a sql query in PHP?
function NewUser()
{
$firstName = $_POST['firstName'];
$lastName = $_POST['lastName'];
$age = $_POST['age'];
$email = $_POST['email'];
$password = $_POST['pass'];
$query = "INSERT INTO users (firstName,lastName,age,email,pass) VALUES ('$firstName','$lastName','$age','$email','$password')";
$db->exec($query);
echo"user created";
}
Thanks

Answer 1

You just write queries, but forgot to execute
$db = new PDO ("mysql:host=localhost;dbname=car_rental;port=3306","root","");
$query = "INSERT INTO users (firstName,lastName,age,email,pass) VALUES ('$firstName','$lastName','$age','$email','$password')";
$db->query($db); // executes it