Learn Russian: У нас есть новые компьютеры.

In Russian, possession is expressed differently than in English. Instead of saying "we have", you literally say "by us there are". The preposition у (by/at) requires the Genitive case, and the Genitive form of мы (we) is нас.

What is the exact role of есть in this sentence?

есть means "is" or "are" in the sense of existence. The Russian way to say "we have new computers" is literally "by us there are new computers." We use есть here to state that the computers actually exist and are in our possession.

Why does the adjective новый change to новые?

Adjectives must match the noun they describe in gender, number, and case. Because компьютеры (computers) is plural, the adjective changes to its plural form, новые. Both the noun and the adjective are in the Nominative case here because the computers are the grammatical subject of the sentence.

How do we know компьютеры is plural?

The singular dictionary word is компьютер, which is a masculine noun ending in a consonant. The standard way to make masculine nouns plural in Russian is to add -ы at the end.