Learn Icelandic: Hvolpur Einars borðaði skóinn.

In Icelandic, the possessor (the word in the genitive case, like Einars) usually comes after the thing being owned. So instead of saying 'Einar's puppy', you say 'puppy Einar's' (Hvolpur Einars).

How do we know to add -s to Einar?

Einar is a masculine name. Most regular masculine nouns and names take an -s ending in the genitive case to show possession. In this specific case, it looks and works exactly like adding an 's' in English!

Why is the word for 'shoe' skóinn here instead of skór?

Two things are happening! First, the shoe is the direct object being eaten, so it changes to the accusative case (from skór to skó). Second, we need to say 'the' shoe, so we attach the masculine accusative definite article -inn to the end, creating skóinn.

Is borðaði the past tense of borða (to eat)?

Yes! The puppy is a 'he/she/it' subject. To form the past tense for this subject with a regular verb like borða, we add the past tense ending -ði, giving us borðaði (ate).