Form

<form method="post">
    Username: <input type="text" name="username"> <br>
    Password: <input type="password" name="password"> <br>
              <input type="submit" name="submit">
</form>

<?php
$serverName = "localhost";
$dbUsername = "root";
$dbPassword = "";
$dbName = "test";

if (isset($_POST['submit'])) {
    $username = $_POST['username'];
    $password = $_POST['password'];

    // Create connection
    $conn = new mysqli($serverName, $dbUsername, $dbPassword, $dbName);

    // Check connection
    if ($conn->connect_error) {
        die("Connection failed: " . $conn->connect_error);
    }

    $sql = "INSERT INTO users (username, password) VALUES ('$username', '$password')";

    if ($conn->query($sql) === TRUE) {
        echo "New record created successfully";
    } else {
        echo "Error: " . $sql . "<br>" . $conn->error;
    }
    $conn->close();
}