If you mean adding users programmatically, you can use the function qa_create_new_user
You can run that from a separate PHP script. See here for using external code, the create user function looks like this:
// basic version
qa_create_new_user($email, $password, $handle);
// or advanced version
qa_create_new_user($email, $password, $handle, $level, $confirmed);
See qa-include/app/users-edit.php line 148.