breakfast
Das Frühstück is the German word for breakfast. It is a noun and is used to refer to the first meal of the day. It is a compound word made up of 'früh' (early) and 'Stück' (piece), literally meaning 'early piece'. It is often used in sentences like 'Ich esse jeden Morgen ein Frühstück' (I eat breakfast every morning).
I have already prepared breakfast.
This sentence is in the perfect tense which is often used in German to talk about actions that have been completed. Here it is being used to imply that the action of preparing breakfast has already been completed.
What would you like for breakfast?
This sentence is using the verb 'möchten' which is a modal verb used to express desire. The preposition 'für' corresponds with the English 'for'.
Breakfast is the most important meal of the day.
This sentence is a simple, declarative sentence. The verb 'ist' corresponds to 'is' in English, and 'die wichtigste Mahlzeit des Tages' literally translates to 'the most important meal of the day'.