You upload your image files directly from your computer to the Tapastic site - no other web pages are necessary. The file specifications are available to read on the upload page, which you access by clicking the cloud icon in the top-right corner of the main site. You can add a new series there, or by visiting your dashboard, which is one of the menu options available when you click your user icon (next to the cloud icon).
If you're posting stand-alone, single page cartoons, I would recommend putting them all in one series. A series doesn't have to be an ongoing story - there are lots of daily gag comics on the site that skip between different themes, characters and settings. Stick to a unified art style and presentation, and your readers won't mind the lack of continuity between episodes.