Login at the administration page of the blog: http://blog.stud.uni-goettingen.de/deinblogname/wp-admin.

At the menu item “Artikel” (“article”), click on “Kategorie” (“category”).

Insert the name and slug (the url-version of the name) of the category. Under “Übergeordnet” (“superior”), choose whether you want to create a main category (choose “Keine” (“none”) as superior category) or a sub-category (choose the respective main category).

Save settings by clicking on “Neue Kategorie erstellen” (“create new category”).

Please note: As a rule all categories are listed in alphabetical order. At the menu item “Artikel”–> “Kat.-Reihenfolge” (“article”–> “order of categories”) you are able to change the order of the existing categories.