Learn German: Das Frühstück ist fertig.

In English, we just say "Breakfast" but in German, meals often take a definite article (der, die, or das). That is why we say Das Frühstück (The breakfast) here.

Where would I put an adverb of frequency like immer (always) in this sentence?

If you want to say "Breakfast is always ready," the adverb of frequency goes right after the conjugated verb. You would say Das Frühstück ist immer fertig.

Does fertig mean "ready" or "finished"?

It actually means both! Depending on the context, fertig translates to "ready" (like a meal being prepared) or "finished" (like being done with a task). For a meal, "ready" makes the most sense.

What is the literal translation of Frühstück?

It literally translates to "early piece." It comes from combining früh (early) and Stück (piece), originally referring to a piece of bread eaten early in the day.