Get wp_current_user_id using PHP and MySQL

awesome people of the Stack Community!

Like the newbie coder I am, it took many hours but at last I got:

• a HTML form inside wordpress ->
• to submit value to MySQL database ->
• and then store the values inside the table.

This page and form requires a login to use, so what I'm trying to do now is getting the wp_current_user_id stored in a field in the table "order" and the field userID.

Does anyone know if this is possible?

Thanks in advance for any kinds of help. Cheers.

order_confirmation.php

<?php

   $db_name = "dbname";
   $db_user = "username";
   $db_pass = "cool_password";
   $db_host = "hostname";

    include 'config.php';

    $db_conn = connectToDB($db_host, $db_user, $db_pass, $db_name);

    //Get values from the form then -> database
    $sql = mysqli_query($db_conn, "
        INSERT INTO ordre(
            user_fname,
            user_lname,
            user_address, 
            user_email,
            user_phone, 
            service_chosen,
            user_note,
            order_date,
            statusID
        )
        VALUES(
            '".$_POST['user_fname']."',
            '".$_POST['user_lname']."',
            '".$_POST['user_address']."',
            '".$_POST['user_email']."',
            '".$_POST['user_phone']."',
            '".$_POST['service_chosen']."',
            '".$_POST['user_note']."',
            '".date('Y-m-d')."',
            '1' 
        )
    ");

    if($sql == TRUE) {
        echo "<p>Yay it worked</p>"; 
        );

    } else {
        echo "<p>Error: " . mysqli_errno($sql) . "</p>";
    }
?>

config.php

<?php

function connectToDB($db_host, $db_user, $db_pass, $db_name) {

//Create the db connection
$db_conn = new mysqli($db_host, $db_user, $db_pass, $db_name);

//Print out an error if any
if($db_conn->connect_error) {
    die('Error #' . $db_conn->connect_errno . ': ' . $db_conn->connect_error);
} 
else {
    //Connected msg
    echo "Connected: " . $db_conn->host_info;
}
    return $db_conn;
}
?>