Request the url of a channel index
There is no predefined 'index' page for channels. Channels are simply a collection of entries. If you want an index page then you will need to create it: either as a single, as an entry within another structure, or as a stand alone template in your templates directory (i.e. craft/templates/news/index.html or craft/templates/news.html). In any case, the url (or uri) is going to be whatever you have defined it as. (i.e. mysite.com/news/). See craft's routing documentation for more info on how requests are routed.