Creating table in a database

<?php
$server = 'localhost';
$username = 'root';
$password = '';
$db = 'TNW';
$conn = mysqli_connect($server, $username, $password, $db);
if($conn){
$query = "CREATE TABLE `username`(
UserId int(30) NOT NULL AUTO_INCREMENT PRIMARY KEY,
FirstName varchar(30) NOT NULL,
LastName varchar(30) NOT NULL,
UserName varchar(30) NOT NULL,
Password varchar(50) NOT NULL
)";
$query_run = mysqli_query($conn, $query);
if($query_run){
echo 'Successfully created a table.';
}else{
echo 'Creating a table Error.';
}
}else{
echo 'Connecting to a database Error.';
}
?>