How to know what the parameters are for Moodle Webservices' functions such as core_user_create_users

Using curl, I'm trying to make a rest call to the web service function to create a user. However, I'm oblivious as to what the required parameters are and can't find any documentation on this. I'm getting the error: > url: mymoodle/webservice/rest/server.php?wstoken=304632866235d8239cd7bf41809dcd03&wsfunction=core_user_create_users&criteria[0][key]=username&criteria[0][value]=name&criteria[1][key]=password&criteria[1][value]=password<br/><br/> Invalid parameter value detected Missing required key in single structure: users