<?php
if(isset($_POST['submit'])){
    $username = $_POST['usernameinput'];
    $password = $_POST['passwordinput'];

    $servername = "localhost";
    $username = "USERNAMECENSOR";
    $password = "PASSWORDCENSOR";
    $dbname = "database";

    try {
        $conn = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);
        // set the PDO error mode to exception
        $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
        $sql = "INSERT INTO accounts (username, password)
        VALUES ('$username', '$password')";
        // use exec() because no results are returned
        $conn->exec($sql);
        echo "Success";
    }
    catch(PDOException $e)
    {
        echo $sql . "<br>" . $e->getMessage();
    }
    $conn = null;
}
?>

<form method="POST" action="">
    <input type="text" name="usernameinput"><br>
    <input type="password" name="passwordinput"><br>
    <input type="submit" class="button" value="Sign in">
</form>