Categories are an important feature on wikis. Creating a category is easy: you just have to write a category name onto the page and you are done. MoinMoin even simplifies this by letting you choose from a list of available categories while you are editing the page. By the way, this page is in the category CategoryCategory.
On the page of the category, you can give a brief description of the category's contents. If you want to get a list of all pages in that particular category, either click the title of the category or insert a suitable macro which lists the pages:
<<FullSearch(CategorySamples)>> lists all pages in the category CategorySamples (alternative you can use <<FullSearch(@PAGE@)>>)
<<FullSearch(r:CategoryRecipes\b -r:CategoryCake\b)>> lists every recipe if it is not about a cake
See HelpOnSearching for further information about the syntax.
Normally, categories have to be named like CategorySomething. If you want to allow other patterns like CatégorieGaffeur (that is French by the way), then the administrator needs to change the configuration option page_category_regex according to the users' language. In a hebrew wiki, you would use page_category_regex = '^Category[A-Z]|^קטגוריה .+'. See HelpOnConfiguration.
The best choice is to create category pages from a CategoryTemplate (see HelpOnTemplates).