This is the "GlossaryCategoryEntry" form. Its purpose is to create and edit Category (vs. instance) Level entries if a page with that name already exists, you will be sent to a form to edit that page.
Note that Mediawiki page names are case sensitive, with the exception of the first character. As an example, the pages Category:Applecore and Category:applecore reference the same category, but Category:Applecore and Category:appleCore do not. Also note that embedded spaces and undescores ('_') are considered identical. This Category:Apple Core and Category:Apple_Core both reference the same page.
To create a page with this form, enter the new category in the form Category:<category name>.