Pages in a category normally display in alphabetical order like that on Category: pages.
If they don't, it's probably because you have Category Exhibition enabled on your wiki (see Help:Category), a feature that admins can enable/disable in Special:WikiFeatures.
In Category Exhibition, pages in the category will display as image thumbnails, instead of an alphabetical list of names.
If you aren't an admin, you won't be able to disable Category Exhibition. But you can switch back to the list view on single category pages by clicking a little icon in the upper-right corner of the page (near the sorting menu).