destruk is right. One thing that confused me early on was "what file do I upload?"
You upload a zip file that contains the manifest at its root, and will also likely contain folders such as images/ and source/
Zip that folder (again, the one with manifest in the root) using a tool such as 7-zip on windows. Then upload that file to your Roku box using the Developer Web Page on your Roku Streaming Player. This action is called "side-loading" your application.
Once your application is side-loaded (aka "loaded") into your Roku, again use the developer web page to then download the .pkg file from your Roku. That .pkg file is what you upload to the Roku web site to make your channel available to others. The package you upload is generated the same way whether you are uploading for a beta period, a private channel, a public channel, or a paid channel.