Are you just wanting to test the theory out? If so, then just put the id.twitch.tv/oauth2/authorize link in your browser and it will attempt a redirect and provide a token that you can use. For example, when I go to the link in my browser for one of my test applications and then read the address bar:
http://morpheus.int.XXXX.net/iobotauth/#access_token=1971skckr..............&scope=chat_login
If you want to build out an entire solution for other folks to come to and authenticate so that you may provide statistics to them for subscribers then you will need to setup a landing page (based on the callback URL you gave to Twitch) that collects the token and stores it for retrieving data.
Again, keep in mind that you may only look at your subscribers when you authenticate, you cannot view the subscribers of anyone else unless they choose to authenticate to your service.
Cheers