https://jquery.com/download/

https://github.com/1000hz/bootstrap-validator

HTML :

<!-- Start Contact Form -->
<form role="form" id="contactForm" class="contact-form" data-toggle="validator" class="shake">
  <div class="form-group">
    <div class="controls">
      <input type="text" id="name" class="form-control" placeholder="Name" required data-error="Please enter your name">
      <div class="help-block with-errors"></div>
    </div>
  </div>
  <div class="form-group">
    <div class="controls">
      <input type="email" class="email form-control" id="email" placeholder="Email" required data-error="Please enter your email">
      <div class="help-block with-errors"></div>
    </div>
  </div>
  <div class="form-group">
    <div class="controls">
      <input type="text" id="msg_subject" class="form-control" placeholder="Subject" required data-error="Please enter your message subject">
      <div class="help-block with-errors"></div>
    </div>
  </div>
  <div class="form-group">
    <div class="controls">
      <textarea id="message" rows="7" placeholder="Massage" class="form-control" required data-error="Write your message"></textarea>
      <div class="help-block with-errors"></div>
    </div>  
  </div>

  <button type="submit" id="submit" class="btn btn-effect"><i class="fa fa-check"></i> Send Message</button>
  <div id="msgSubmit" class="h3 text-center hidden"></div> 
  <div class="clearfix"></div>   

</form>     
<!-- End Contact Form -->

JS :

$("#contactForm").validator().on("submit", function (event) {
    if (event.isDefaultPrevented()) {
        // handle the invalid form...
        formError();
        submitMSG(false, "Did you fill in the form properly?");
    } else {
        // everything looks good!
        event.preventDefault();
        submitForm();
    }
});


function submitForm(){
    // Initiate Variables With Form Content
    var name = $("#name").val();
    var email = $("#email").val();
    var msg_subject = $("#msg_subject").val();
    var message = $("#message").val();


    $.ajax({
        type: "POST",
        url: "assets/php/form-process.php",
        data: "name=" + name + "&email=" + email + "&msg_subject=" + msg_subject + "&message=" + message,
        success : function(text){
            if (text == "success"){
                formSuccess();
            } else {
                formError();
                submitMSG(false,text);
            }
        }
    });
}

function formSuccess(){
    $("#contactForm")[0].reset();
    submitMSG(true, "Message Submitted!")
}

function formError(){
    $("#contactForm").removeClass().addClass('shake animated').one('webkitAnimationEnd mozAnimationEnd MSAnimationEnd oanimationend animationend', function(){
        $(this).removeClass();
    });
}

function submitMSG(valid, msg){
    if(valid){
        var msgClasses = "h3 text-center tada animated text-success";
    } else {
        var msgClasses = "h3 text-center text-danger";
    }
    $("#msgSubmit").removeClass().addClass(msgClasses).text(msg);
}

PHP : 

$errorMSG = "";

// NAME
if (empty($_POST["name"])) {
    $errorMSG = "Name is required ";
} else {
    $name = $_POST["name"];
}

// EMAIL
if (empty($_POST["email"])) {
    $errorMSG .= "Email is required ";
} else {
    $email = $_POST["email"];
}

// MSG SUBJECT
if (empty($_POST["msg_subject"])) {
    $errorMSG .= "Subject is required ";
} else {
    $msg_subject = $_POST["msg_subject"];
}


// MESSAGE
if (empty($_POST["message"])) {
    $errorMSG .= "Message is required ";
} else {
    $message = $_POST["message"];
}

//Add your email here
$EmailTo = "hello@example.com";
$Subject = "New Message Received";

// prepare email body text
$Body = "";
$Body .= "Name: ";
$Body .= $name;
$Body .= "\n";
$Body .= "Email: ";
$Body .= $email;
$Body .= "\n";
$Body .= "Subject: ";
$Body .= $msg_subject;
$Body .= "\n";
$Body .= "Message: ";
$Body .= $message;
$Body .= "\n";

// send email
$success = mail($EmailTo, $Subject, $Body, "From:".$email);

// redirect to success page
if ($success && $errorMSG == ""){
   echo "success";
}else{
    if($errorMSG == ""){
        echo "Something went wrong :(";
    } else {
        echo $errorMSG;
    }
}