Потрібно заповнити і відправити форму<form action="index.php" method="POST">
    <label for="firstName">First Name:</label>
    <input type="text" id="firstName" name="firstName" required><br>

    <label for="lastName">Last Name:</label>
    <input type="text" id="lastName" name="lastName" required><br>

    <label for="phone">Phone:</label>
    <input type="text" id="phone" name="phone" required><br>

    <label for="email">Email:</label>
    <input type="email" id="email" name="email" required><br>

    <button type="submit">Submit</button>
</form>