Learn Croatian: Tražimo vozača. - We are looking for the driver.

Because vozač (driver) is the direct object of the verb tražimo (we are looking for), so it must be in the accusative case. For masculine nouns that are living beings (animate), the accusative case adds an -a to the end. If we were looking for a non-living masculine noun, it would stay exactly the same as its dictionary form.

The English translation says "looking for," but there is no word for "for" in the Croatian sentence. Why?

The Croatian verb tražiti translates to "to look for" or "to seek." The idea of "for" is already built into the verb itself, so you do not need an extra preposition. You just follow the verb directly with the object you are seeking.

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

The pronoun mi (we) is left out here, which is very common in Croatian. The verb ending -mo in tražimo already clearly shows that "we" are the ones doing the looking, making the pronoun unnecessary.

How do we know it means "the" driver and not "a" driver?

Croatian does not use articles like "a" or "the". Depending on the situation, Tražimo vozača could mean either "We are looking for the driver" (a specific one you already talked about) or "We are looking for a driver" (just hiring anyone for the job).