If the page you're seeing in [dmoz.org...] , it means that the category in question does not accept submissions. This is frequently done when the category is what's called an "@link farm" (where it just contains links to other categories and doesn't contain any sites of its own) or when the category has subcategories that all submissions should be made to.
If the category is actually accepting submissions, then you'll see an information page titled "Submit a Site to the Open Directory" (that you should read) with a button at the bottom to click to agree "I have read and understand the submissions guidelines, and I'm ready to submit my site" -- that will take you to the actual submission screen..
And finally, are you actually using the links on [dmoz.org...] and not one of our downstream data users? Some users of our data have links that send you there rather than to the submission form for the category.