$name = $entity->title; //fill it with what field you want
$email = $entity->YOUR_EMAIL_FIELD_MACHINE_NAME['und'][0]['value'];
$pass = $entity->YOUR_PASS_FIELD_MACHINE_NAME['und'][0]['value'];
$new_user = array(
  'name' => $name,
  'pass' => $pass, // note: do not use md5
  'mail' => $email,
  'status' => 1,
  'init' => $email,
  'roles' => array(
    DRUPAL_AUTHENTICATED_RID => 'authenticated user',
  ),
);

// The first parameter is sent blank so a new user is created.
user_save('', $new_user);