Learn Croatian: Autobus i taksi idu u grad. - The bus and the taxi go to the city.

Idu is the "they" form (third-person plural) of the verb ići (to go). Even though autobus (bus) and taksi (taxi) are both singular nouns, connecting them with i (and) creates a plural subject: "the bus and the taxi" equals "they".

How do we know u grad means "to the city" and not "in the city"?

With verbs of motion like ići (to go), the preposition u indicates moving "to" or "into" a destination. When showing motion toward a place, u triggers the accusative case. If there were no movement (for example, "The bus is parked in the city"), you would use the locative case instead.

Why doesn't the word grad change its ending for the accusative case here?

For masculine nouns that are inanimate (non-living objects), like grad (city), the accusative form looks exactly the same as the basic dictionary form. If the masculine noun were a living being (like a person or an animal), it would take an -a ending instead.

Why is "taxi" spelled as taksi?

The Croatian language is highly phonetic, meaning words are written exactly as they are pronounced. Since the Croatian alphabet does not include the letter "x", the sound is spelled out using ks. You will see this rule applied often with borrowed international words.