Learn Turkish: Kaz her sabah bir altın yumurta verirmiş. - The goose would give a golden egg every morning.

This is the Inferential Aorist. It combines the aorist suffix -ir (used for general facts or repeated actions) with the storytelling/inferential suffix -miş. In this sentence, it shows a repeated past action ("would give") that belongs to a fable or a story we didn't personally witness.

What is the difference between saying verirmiş and verirdi?

While both can translate to "would give" or "used to give", verirdi (aorist + -di) is used for factual past habits that you know for certain or witnessed. Verirmiş is specifically used for hearsay, legends, or fairy tales, which perfectly fits this sentence about a magical goose.

Why is yumurta in its bare form instead of taking the accusative case (yumurtayı)?

Because it is an indefinite direct object. The goose gives a golden egg (bir altın yumurta), not the golden egg. Indefinite objects do not take the accusative suffix and must be placed directly before the verb.

Altın is a noun meaning "gold". Why doesn't it need a suffix to become the adjective "golden"?

In Turkish, nouns that refer to materials can act exactly like adjectives without any changes. You just place the material directly before the item. Altın (gold) + yumurta (egg) naturally creates altın yumurta (golden egg).