U lokativu razgovaramo o gradu, a u instrumentalu putujemo s prijateljicom.

It is showing how different prepositions trigger different cases in Croatian:

• o + locative: razgovaramo o gradu = we are talking about the city
• s + instrumental: putujemo s prijateljicom = we are traveling with a female friend

It also includes the phrases u lokativu and u instrumentalu, which mean in the locative and in the instrumental.

Because the preposition u usually means in and here it is used metaphorically, as in in the locative or in the instrumental.

So the case names themselves have to change form:

• lokativ → u lokativu
• instrumental → u instrumentalu

This is the locative singular form after u.

Because the preposition o meaning about requires the locative case.

The noun is:

• nominative: grad = city
• locative singular: gradu

So:

• o gradu = about the city

You should think of o as a preposition that automatically calls for the locative.

Because s meaning with requires the instrumental case.

The noun is:

• nominative: prijateljica = female friend
• instrumental singular: prijateljicom

So:

• s prijateljicom = with a female friend

Again, the preposition determines the case.

Yes, u can take either the locative or the accusative, depending on meaning.

• u + locative = location, being in something
• u + accusative = motion into something

Here, u lokativu and u instrumentalu mean in the locative and in the instrumental, so this is a location/state idea, not motion. That is why the locative is used.

Compare:

• u gradu = in the city
• u grad = into the city (less common than u grad / u grad? Actually standard is u grad for motion with accusative)

A is a coordinating conjunction. In this sentence it has a contrastive or parallel meaning, something like:

• and
• while
• whereas

So the sentence sets up a comparison:

• In the locative, we talk about the city, and in the instrumental, we travel with a female friend.

It links two matching grammatical examples.

Because Croatian often uses the present tense to state general facts or explain grammar rules.

Here the sentence is not talking about one specific real-life event. It is giving examples of how cases work, so present tense is natural:

• razgovaramo = we talk / we are talking
• putujemo = we travel / we are traveling

They are both 1st person plural forms, with the subject mi = we understood and left unstated.

No. Gradu can be both:

• dative singular
• locative singular

This is very common in Croatian: some case forms look the same.

How do you know which one it is? From the context, especially the preposition.

• o gradu must be locative, because o takes the locative.
• If you had something like prilazim gradu = I am approaching the city, that would be dative.

Both mean with, but sa is mainly used to make pronunciation easier.

You often hear sa before words beginning with certain consonants or consonant clusters, especially where s would be awkward to pronounce.

Examples:

• sa sestrom
• sa školom
• sa mnom

But here s prijateljicom is perfectly normal and standard, because it is easy to pronounce.

Yes. The base noun prijateljica is feminine and means female friend.

Compare:

• prijatelj = male friend
• prijateljica = female friend

So:

• s prijateljem = with a male friend
• s prijateljicom = with a female friend

Croatian marks gender more explicitly than English often does.

Because Croatian does not have articles like English the and a/an.

So:

• grad can mean a city or the city
• prijateljica can mean a female friend or the female friend

The exact meaning depends on context.

Yes, absolutely. The case is not a permanent property of the noun. It changes depending on its role in the sentence and on the preposition used.

For example, with grad:

• grad = nominative
• o gradu = locative, after o
• u gradu = locative, after u
• s gradom = instrumental, after s

And with prijateljica:

• prijateljica = nominative
• o prijateljici = locative
• s prijateljicom = instrumental

So the key question is not just what is the noun? but also what preposition or function does it have here?