Help:Categories and namespaces
The FHB wiki uses the additional namespace Recipe for grouping, well, recipes. All you have to do when creating a new one, is to prefix the page title with "Recipe:", like Recipe:Khlav_Kalash. It will be listed in the recipe index automatically (may take up to 6 hours). Further subgrouping via categories is planned, but not implemented yet.
In the main namespace, without prefix, categories are currently used for
To mark a page to belong to one or more categories, just add a tag at the bottom when editing:
Have a look at the existing pages for examples.