Learn Icelandic: Er kötturinn úti?

Just like in English, Icelandic makes a "yes/no" question by swapping the subject and the verb. A normal statement would be Kötturinn er úti (The cat is outside). By moving the verb Er to the very front of the sentence, it becomes the question Er kötturinn úti? (Is the cat outside?).

Where is the word for "the" in this sentence?

Icelandic usually doesn't use a separate word for "the" like English does. Instead, it gets attached directly to the end of the noun. The base word is köttur (a cat). By adding the ending -inn, it becomes kötturinn (the cat).

Why does kötturinn end with -inn instead of a different ending like -ið?

The ending you use for "the" depends on the grammatical gender of the noun. Because köttur is a masculine word, it takes the masculine ending -inn. If it were a neuter word, it would take -ið, and a feminine word would take -in.

I've also seen út used for "outside". Why do we use úti here?