How can I get the data from a form by means of javascript or AJAX?

Google translate:

I'm making a web page, and I want to schedule a comment section to it, that contains the date and time the user commented. Being a first-timer in the subject, I'm doing badly using the JavaScript language for that case; Also AJAX. I wish that once the data is sent to MYSQL, it will be returned to the page.

Google translate:

This is my HTML code:

<form name="f_coment" action= "insertar.php" method="POST">
    <Label for="nombre">Nombre:</Label>
    <input type="text" name="nombre" required=""placeholder="Escribe tu nombre..."><br>
    <label for="email">Email:</label>
    <input type="email" name="email"  required=""placeholder="Escribe tu email..."> <br>
    <label for="clave">Clave:</label>
    <input type="password" name="clave" required="" placeholder="Escribe tu clave..."><br>
    <label for="comentario">Comentario:</label>
    <textarea type="comentario" name="comentario" cols="90px" rows="8" required="" placeholder="Escriba aquí su comentario..."></textarea><br><br>
    <input type="submit" value="comentar" id="comentar">
</form>

Google translate:

This is my PHP code:

<?php 
    error_reporting(0);
    
    $PDO = new PDO('mysql:host=localhost;dbname=db_comentarios;charset=UTF8','root','' );
    try { 
        echo "datos enviados correctamente";
        $sql=$PDO->prepare("INSERT INTO prueba1(nombre, email, clave, comentario) VALUES (:nombre, :email, :clave, :comentario)");
        $sql->bindParam(':nombre',$_POST['nombre']);
        $sql->bindParam(':email',$_POST['email']);
        $sql->bindParam(':clave', password_hash($_POST['clave'], PASSWORD_DEFAULT));
        $sql->bindParam(':comentario',$_POST['comentario']);
        $sql->execute();
    }catch(PDOException $e) {
        echo "Fallo de conexion al enviar los datos:".$e->getMessage();
    }
?>

Google translate:

I would really appreciate any help.

Quote:

This is a piece of Java code that I could try:

function getFormValues{
    var nombre = document.f_coment.nombre.value;
    var email = document.f_coment.email.value;
    var clave = document.f_coment.clave.value;
    var comentario = document.f_coment.comentario.value;
}