Learn Dutch: Ik koop een banaan en een appel. - I am buying a banana and an apple.

In Dutch, when you want to negate a noun that uses een (a/an), you replace it with geen (no / not a). To say "I am not buying a banana," you simply change een banaan to geen banaan: Ik koop geen banaan.

The translation says "I am buying". Where is the word for "am"?

Dutch doesn't use a separate word for "am" when describing a present action. The simple verb koop means both "buy" and "am buying". So Ik koop does the job of both!

How is the word een pronounced here?

It is pronounced with a short, soft "uh" sound, exactly like "un" in English. Don't let the double 'e' trick you! It is only pronounced with a long "ay" sound if it has accent marks (één), which specifically means the number one.

Do I need to know if banaan and appel are de or het words to use een?

No! While they both happen to be de words (de banaan, de appel), the indefinite article een (a/an) is exactly the same for all singular nouns, regardless of their gender.