// functions.php
<?php include 'connect.php'; ?>
function createData() {
    global $connection;
    $username = mysqli_real_escape_string($connection, $username);
    $password = mysqli_real_escape_string($connection, $password);

    $hashFormat = '$2y$07$';
    $salt = 'usesomesillystringforsalt$';
    $hashF_salt = $hashFormat . $salt;
    $password = crypt($password, $hashF_salt);

    $query = "INSERT INTO users(username, password) ";
    $query .= "VALUES('$username', '$password')";
    $result = mysqli_query($connection, $query);
    if(!$result) {
      die(mysql_error());
    } else {
      echo "Created";
    }
  }

// create.php
<?php include "functions.php"; ?>
if(isset($_POST['submit'])) {
  $username = $_POST['username'];
  $password = $_POST['password'];

  if($username && $password) {
    createData();
  } else {
    echo "Input can not be blank";
  }
}