Help:Category
(Hindi)
Note: Categories work only in WikiMedia version 1.3 and later.
The Category namespace consists of pages which each represent a so-called category. You can place a page in a category by adding [[Category:foobar]] to the page's wikitext (where foobar is the name of the category).
For example to add an article called Albert Einstein to the category "people" you would edit the article and add "[[Category:People]]".
Where this line is added does not matter for the software, but e.g. on Wikipedia the rule is to put it at the end of the text, but above any interlanguage links.
The page of the category contains text that can be edited, like any other page, but when displaying the page, the last part of what is displayed is an automatically generated, alphabetical list of all pages in that category.
Sub-categories
Categories themselves can also be specified to belong to another category. When displaying the page of a category to which other categories belong, a separate automatically generated, alphabetical list of sub-categories is also produced.
For example you could edit [[Category:Soccer]] and add the link [[Category:Sports]]. The Soccer category would then be a sub-category of the Sports category.
Categories to which a page belongs
Pages, including categories, can belong to more than one (other) category. The categories to which a page belongs are displayed in a fixed place, depending on the skin (the bottom for Monobook, the upper right corner for Standard), regardless of where in the wikitext they are specified.
Existing categories
You can see currently used categories for each project with Special:Categories, for Wikipedia en:Special:Categories. It produces a list of all categories, including those which contain subcategories or pages, but have no additional text. In that case a link to the category page shows up as link to a non-existing page that leads to the edit page. Avoiding this complication is an additional reason for entering in a category page at least a link to the main article on the field and a reference to a higher category to which it belongs.
Setting sort keys
If you want the article, in the list of articles in the category, to be positioned alphabetically by something other than its name you should use the following link form: [[Category:foobar|sort key]] (where foobar is the category name and sort key is the value to sort by).
For example to add an article called Albert Einstein to the the category "people" and have the article sorted by "Einstein, Albert" you would type "[[Category:People|Einstein, Albert]]".
The sort keys are case sensitive, so [[Category:The Foobar|Foobar]] is sorted before [[Category:The Bar|bar]].
Linking to a category
If you want to link to a category without the current article being added to it you should use the following link form [[:Category:foobar]] (where foobar is the category name), note the extra : before Category.
Relation with "What links here"
A category is somewhat like a "What links here" page with regard to the special category links.
However, "What links here" tends to be a by-product of links that are useful anyway (although links may be put with this use in mind), while category links are put specially to produce a category page.
Linking from a test page, user page, etc. to a category is considered to pollute the category, while regular links from such pages showing up in "what links here" is considered harmless.
Category listings are alphabetical, for "What links here" this typically applies for the first part only, for the pages already linking to the given page at the time of the last rebuilding of the link tables in the database.