Let's take the phrase "what do you need, older?". Here the word "old man" stands in the cognitive case. Or "head of garlic", "a piece of sugar" - the words are used in the second genitive case, or in the quantitative-separative.
Some words have several forms of prepositional case. For example, "in the closet" and "about the cabinet" - in the first case it is spoken about the local case. When they say about the place where the route starts, some words form the initial case - for example, "left the forest".