Absolute Simplest Way to Set Up Basic API

I've created an Application while going through the tutorial.
I have an App ID.
I have an App Secret Token.

How am I supposed to develop a redirect URL (URI)?

Request authorization code by using POST method on:
https://www.humanity.com/oauth2/token.php

{"error":"invalid_request","error_description":"The request method must be POST when requesting an access token","error_uri":"http://tools.ietf.org/html/rfc6749#section-3.2"}

Where can I set up POST?

Is there some sample code somewhere that I can custom tailor for my companies needs?