Ask Wessen?
Find the owner.

One question. One answer. That answer is always Genitiv. Possession has a question word built for it. Use it and the owner surfaces every time.

Related: The German Genitiv Case, the full picture of possession. The words that usually answer this question: Possessive pronouns. Whose is it?

Wessen? means: who does this belong to?

Wessen means "whose." You point it at any noun and ask: who owns this? Who does this belong to? The word that answers is always Genitiv. In edupango, it is always pink.

Three sentences. Same question every time:

• Das ist dasAuto meines Vaters. Wessen Auto? → meines Vaters.
• DieTasche derLehrerin liegt hier. Wessen Tasche? → derLehrerin.
• Ich lesedasBuch meiner Schwester. Wessen Buch? → meiner Schwester.

In every case, the answer is pink. Something belongs to it. There is an owner.

The Genitiv is possession

The Nominativ does the action. The Akkusativ receives it. The Dativ is the recipient. The Genitiv is none of these. It shows who or what something belongs to. It is the ownership case. The relationship between two nouns, made visible.

Two nouns. One owns the other:

• DasHaus desMannes ist groß. (The man's house is big.)
• DerTitel desBuches war bekannt. (The title of the book was well known.)
• DieStimme desKindes war laut. (The child's voice was loud.)

The Genitiv noun always follows the thing it belongs to. First the thing, then the owner.

The articles change here too

The Genitiv has its own article forms. Masculine and neuter take des and the noun usually gets an -s or -es ending: except for the weak masculine nouns, which take -n or -en instead: desStudenten, desJungen, desHerrn. Feminine and plural take der with no change to the noun.

Gender	Nominativ	Genitiv
Masculine	derMann	desMannes
Feminine	dieFrau	derFrau
Neuter	dasKind	desKindes
Plural	dieLeute	derLeute

The pattern: masculine and neuter add -s or -es to the noun. Feminine stays the same. Plural stays the same. The article does the work.

Written vs. spoken German

The Genitiv is more common in written and formal German. In everyday speech, Germans often replace it with von + Dativ. Both are correct. Both mean the same thing.

• DasAuto meines Vaters is formal and written.
• DasAuto von meinem Vater is spoken and casual.

You need to understand both. The Genitiv appears constantly in texts, news articles, and formal writing.