I understand what you need. You need categories to show up as a page when clicked on them right?
For example: You have a category named "Themes" on your site "www.website.com" now you want "www.website.com/themes" to open up as a page and not as a error page which wordpress shows as default.
Unfortunately this is not possible but I can give you a way out to this problem. In the method I'm describing you will have to set up every the content in Wordpress pages and not as Wordress Posts. You can create page with the name "Themes", You can write or design whatever you wanted to show on that category page. Just assume the page named "Theme" to be a category. Now create another page under theme named "Theme 1"(You wanted to show this under the category "Theme") and design or write whatever you wanted to write there. Currently the URL of "Theme 1" is "www.website.com/theme-1" but we want it as "www.website.com/Theme/Theme-1". Follow these steps now:
To do this just open the Page directory in wordpress i.e. "All Pages", Click on "Quick Edit" under "Theme 1". Set its parent page as "Theme". Now click "View" and you will see the desired breadcrumb navigation. Revert back if you have any problems.