The web publishing wizard is essential to be able to upload page groups onto Webstore. It should already be installed on your organisation's machines, but you may need to check if you wish to use a computer at home for example.
If you don't have it installed, it is quick and easy to download and install.
The web publishing wizard should appear on each of the upload pages, looking like this:
e.g. On the Novice - Add web page without a subfolder page:-
If for any reason it is greyed out, or doesn't appear at all, you will need to download and install it. See Downloading and Installing the Web Publishing Wizard.