使用(SELECT)和(INSERT INTO)从PHP表单将数据插入MySQL数据库

I have a class where I need to create a website with PHP and MySQL databases. The problem is that I am not able to insert data from PHP form in my database. The user is asked to write their username and their password, after he is asked to write different values that are going to be inserted in the database. With the username and the password, I need to find the Id of the user. With that Id, I need to insert the values entered by the user of the website into the table PERSONNAGE with the IdUser of the row being the one from the user's username and password. Here's an exemple to explain myself better :

<form action="backend.php" method="POST">
        <fieldset>
            <legend>Creation Personnage</legend>

            <label> Username :
                <input type="text" name="nom" id="nom" />
            </label>

            <label> Password :
            <input type="text" name="mdp" id="mdp" />
            </label>

            <br><br><br><br>

            <label> Race :
            <input type="text" name="race" id="race" />
            </label>

            <label> Classe :
            <input type="text" name="classe" id="classe" />
            </label>

            <br><br>

            <label> Niveaux :
            <input type="text" name="niveaux" id="niveaux" />
            </label>

            <label> Experience :
            <input type="text" name="experience" id="experience" />
            </label>

            <br><br>

            <label> Sexe :
            <input type="text" name="sexe" id="sexe" />
            </label>

            <label> Age :
            <input type="text" name="age" id="age" />
            </label>

            <br><br>

            <label> Poids :
            <input type="text" name="poids" id="poids" />
            </label>

            <label> Peau :
            <input type="text" name="peau" id="peau" />
            </label>

            <br><br>

            <label> Cheveux :
            <input type="text" name="cheveux" id="cheveux" />
            </label>

            <label> Yeux :
            <input type="text" name="yeux" id="yeux" />
            </label>

            <br><br>

            <label> Religion :
            <input type="text" name="religion" id="religion" />
            </label>

            <label> Portrait :
            <input type="text" name="portrait" id="portrait" />
            </label>

            <br><br>


        </fieldset>

        <input type="submit" value="Ajouter">
    </div>

Here's the backend.php :

<?php
        error_reporting(E_ALL);
        ini_set('display_errors', 1);
        include_once($_SERVER["DOCUMENT_ROOT"]."/cnxPDO.php");
        if($_SERVER['REQUEST_METHOD'] === 'POST')
        {
            $con = connecPDO("DD", "myparam");
            $nom = $_POST['nom'];
            $mdp = $_POST['mdp'];
            $race = $_POST['race'];
            $classe = $_POST['classe'];
            $niveaux = $_POST['niveaux'];
            $experience = $_POST['experience'];
            $sexe = $_POST['sexe'];
            $age = $_POST['age'];
            $poids = $_POST['poids'];
            $peau = $_POST['peau'];
            $cheveux = $_POST['cheveux'];
            $yeux = $_POST['yeux'];
            $religion = $_POST['religion'];
            $portrait = $_POST['portrait'];

            $idUser = 'SELECT idUser FROM USER WHERE nom = '$nom' AND mdp = '$mdp'';

            $sql='INSERT INTO PERSONNAGE(idUser,race,classe,niveaux,experience,sexe,age,poids,peau,cheveux,yeux,religion,portrait) 
                    VALUES(:idUser,:race,:classe,:niveaux,:experience,:sexe,:age,:poids,:peau,:cheveux,:yeux,:religion,:portrait)';

            $stmt = $con->prepare($sql);
            $stmt->BindParam(':idUser',$idUser);
            $stmt->BindParam(':race',$race);
            $stmt->BindParam(':classe',$classe);
            $stmt->BindParam(':niveaux',$niveaux);
            $stmt->BindParam(':experience',$experience);
            $stmt->BindParam(':sexe',$sexe);
            $stmt->BindParam(':age',$age);
            $stmt->BindParam(':poids',$poids);
            $stmt->BindParam(':peau',$peau);
            $stmt->BindParam(':cheveux',$cheveux);
            $stmt->BindParam(':yeux',$yeux);
            $stmt->BindParam(':religion',$religion);
            $stmt->BindParam(':portrait',$portrait);

            if (!$stmt->execute()) {
            echo "<br>PDO::errorCode():";
            print_r($stmt->errorCode());
            echo "<br>PDO::errorInfo():";
            print_r($stmt->errorInfo());
            }
            else { echo " <br> Sauvegarde effectuée";  }
        }
    ?>

I really need help to finish this or I won't pass my class !! The fact is that our teacher doesn't explain anything about the class and we have to find everything on the web !! I don't understand 3/4 of PHP and MySQL. So I really need some help ! There's also a lot more I need to do, but I will begin with this.

The error directly relates to the fact that there are the wrong amount of variables supplied for the SQL statement parameters. Alternatively, you are trying to update a column which does not exist in the table.

Check the column names match exactly with the supplied column names in the statement, and make sure you supply data only for columns which exist in the table.

Also, if you want PHP to interpolate values iinto variables within your SQL statement, you MUST use double quotes instead of single quotes for your SQL statement. PHP will only interpolate values into variables if you use double quotes.