Learn Croatian: Trebamo manje automobila u gradu. - We need fewer cars in the city.

In Croatian, words that express a quantity require the genitive case. Because we are using manje (fewer or less) to talk about an amount of cars, the noun that follows must be in the genitive.

How do we form the genitive plural for masculine words like automobil?

For regular masculine nouns, the genitive plural is formed by adding -a to the base word. So, automobil becomes automobila.

Doesn't automobila also mean "of a car" in the singular? How do we know it's plural?

Good catch! For regular masculine nouns, the genitive singular and genitive plural are spelled exactly the same. We know it means "cars" here strictly from context, because saying "we need less of one car" wouldn't make much sense. In spoken Croatian, the -a at the end of the plural is pronounced slightly longer to tell them apart.

Why does the sentence say u gradu instead of just u grad?

The preposition u (in) is used with the locative case when describing a fixed location. Since grad (city) is a regular masculine noun, it takes the locative ending -u.

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