A stub is an incomplete page or a brief page in need of expansion. You can see a complete list of stub pages here.
If you see a page that needs further expansion, or if you create a page but can not finish it, you can add a “stub” template tag.
For more information, see Wikipedia:Stub.
If you want to indicate that a new page should be created for a topic, simply create a link to that page from some other page. The page will then appear in Special:WantedPages.
If you want the new page to be created in a particular category, then edit the category's page to add a link to the wanted page in this section:
Please create pages for (remove any blue links from this section)
The page will then appear in Special:WantedPages as well as in the category page.