Getting users information from moodle

How to get the section's user information (like name, password)? Is there any method that returns it? I'm trying the function "core_user_get_users_by_field", but it isn't works. That's I've done: String serverurl = url + "/webservice/rest/server.php" + "?wstoken=" + token + "&wsfunction=" + functionName; obs: The server was constructed using REST.