Where do you use the word an in a sentence?

You use the Word "an" when you are would usually use the Word "a," only you're describing a noun that starts with a vowel or a vowel sound.

For example:

I have no idea how I would use this Word in A sentence.

I would like to eat AN Apple.

I have AN hour to get to my train.

My last card was AN ace.

I would like to have A manatee as a pet.