Help with form validation

Hello. I have a problem with form validation because i don't know JS. So I'm asking for help.

Here's the code:

$data=$_POST;
 if(isset($data['do_login']))
 {
 $errors = array();
 if ($data['server'] != "" || isset($data['server']))
 {
 $user = R::findOne($data['server'], 'name = ?', array($data['name']));
 if( $user)
 {
 if(validate_password($data['password'], $user->password))
 {
 $_SESSION['logged_user'] = $user;
 header("Location: https://gov-helper.roffdaniel.com/");
 } else {
 $errors[] = 'Неверный пароль!';
 }
 } else
 {
 $errors[] = 'Аккаунт с таким логином не найден или не существует!';
 }
 } else
 {
 $errors[] = 'Выберете сервер авторизации!';
 }
 }



And form:

<form method="POST" action="https://gov-helper.roffdaniel.com/login/" id="jForm">
<div class="text-center">
<h3 class="dark-grey-text mb-5"><strong>Авторизация</strong></h3>
</div>';
if (!empty($errors)) {
echo'
<div class="card red lighten-1 text-center z-depth-2">
<div class="card-body">
<p class="white-text mb-0">'.array_shift($errors).'</p>
</div>
</div>
<hr class="my-5">
';
}echo'
<!--Body-->
<!--<label for="server" data-error="error">Сервер</label>-->
<select class="mdb-select colorful-select dropdown-primary" name="server" id="server">
<option value="" disabled selected>Выберите ваш сервер</option>
<option value="users_gov_orange">Orange</option>
<option value="users_gov_blue">Blue</option>
</select>

<div class="md-form">
<i class="fa fa-user prefix"></i>
<input type="text" id="name" name="name" class="form-control validate" value = "'.$data['name'].'">
<label for="name" data-error="error">Ваш ник</label>
</div>

<div class="md-form pb-3">
<i class="fa fa-lock prefix"></i>
<input type="password" id="password" name="password" class="form-control validate" value = "'.$data['password'].'">
<label for="password" data-error="error">Ваш пароль</label>

<!--<p class="font-small blue-text d-flex justify-content-end text-center"><a href="#" class="blue-text ml-1">восстановить пароль</a></p>-->
</div>

<div class="text-center mb-3">
<button type="submit" class="btn blue-gradient btn-block btn-rounded z-depth-1a" name="do_login" id="do_login">Войти</button>
</div>
</form>