Learn Icelandic: Bátarnir eru ekki nýir.

Bátarnir means the boats. It starts with the singular masculine noun bátur (a boat). To make it plural, we drop the -ur and add -ar to get bátar (boats). Finally, to say the boats, we add the masculine plural definite ending -nir, resulting in bátarnir.

Why does the adjective for new, nýir, have an -ir ending?

In Icelandic, adjectives must match the noun they describe in gender, number, and case. Since bátarnir is a masculine, plural subject (the nominative case), the base adjective nýr (new) changes to its masculine plural form, which is nýir.

Why is the verb eru used instead of er?

Eru is the plural form of the verb vera (to be) for they are. Because the subject bátarnir (the boats) is plural, the verb must also be plural.

Where does the word ekki go in this type of sentence?

In a simple descriptive sentence, ekki (not) goes right after the verb and before the adjective. The order matches English perfectly here: are (eru) not (ekki) new (nýir).