Moramo paziti kad je pločnik klizav.

Moramo is the 1st person plural present tense of morati, which means must / have to.

So:

• moram = I must
• moraš = you must
• mora = he/she/it must
• moramo = we must
• morate = you (plural/formal) must
• moraju = they must

In this sentence, moramo means we must or we have to.

After the modal verb morati (must / have to), Croatian normally uses the infinitive of the main verb.

So the pattern is:

• morati + infinitive

Examples:

• Moram učiti. = I have to study.
• Moramo paziti. = We have to be careful / We have to watch out.

That is why you get moramo paziti, not moramo pazimo.

In this sentence, paziti means something like:

• to be careful
• to watch out
• to pay attention

It is a very common Croatian verb with a broad range of uses.

For example:

• Pazi! = Watch out! / Be careful!
• Pazim na djecu. = I look after the children.
• Moramo paziti. = We have to be careful.

So here it does not mean simply to look with your eyes. It means to act carefully because there may be danger.

Croatian often drops subject pronouns when they are already clear from the verb ending.

Here, moramo already tells you the subject is we.

So:

• Moramo paziti = We have to be careful

You could say Mi moramo paziti, but mi is usually added only for emphasis, contrast, or clarity.

For example:

• Mi moramo paziti, a oni ne. = We have to be careful, but they do not.

Kad means when.

Yes, it is basically the same as kada.
The shorter form kad is very common in everyday speech and writing.

So these are both natural:

• Moramo paziti kad je pločnik klizav.
• Moramo paziti kada je pločnik klizav.

The meaning is the same. Kada can sound a little fuller or slightly more formal, but both are standard.

Je is the 3rd person singular present tense of biti (to be).

It is used because the subject of the second clause is pločnik (the sidewalk/pavement), which is:

• singular
• masculine

So:

• pločnik je klizav = the sidewalk is slippery

This is just the normal Croatian way to say is.

Pločnik is in the nominative singular because it is the subject of the clause kad je pločnik klizav.

The structure is:

• pločnik = subject
• je = is
• klizav = slippery

So it stays in the nominative.

Because klizav is an adjective and it must agree with pločnik.

Pločnik is:

• masculine
• singular
• nominative

So the adjective must also be:

• masculine
• singular
• nominative

That gives klizav.

Compare:

• pločnik je klizav = the sidewalk is slippery
• cesta je klizava = the road is slippery
• more je klizavo = the sea is slippery

So the ending changes depending on the noun.

Yes, klizav is a normal and common word for slippery.

It comes from the idea of sliding or slipping.

You may also come across sklizak, which can also mean slippery. Both are used, though usage can vary by speaker, region, and context.

In this sentence, klizav sounds completely natural.

Yes. That word order is also correct:

• Moramo paziti kad je pločnik klizav.
• Kad je pločnik klizav, moramo paziti.

Both mean the same thing.

The difference is mainly one of focus and style:

• starting with Moramo paziti emphasizes the need to be careful
• starting with Kad je pločnik klizav emphasizes the condition or situation first

Croatian word order is more flexible than English word order.

It can often mean either when or whenever, depending on context.

In this sentence, kad je pločnik klizav is naturally understood as something like:

• when the sidewalk is slippery
• whenever the sidewalk is slippery

In other words, it expresses a general condition: in situations where the sidewalk is slippery, we need to be careful.

Yes. Croatian has several ways to express this idea.

For example:

• Moramo biti oprezni kad je pločnik klizav. = We have to be careful when the sidewalk is slippery.
• Trebamo paziti kad je pločnik klizav. = We should / need to be careful when the sidewalk is slippery.

But moramo paziti is very natural and idiomatic. It sounds like we need to watch out.

Yes. Paziti is an imperfective verb.

That makes sense here because the sentence describes:

• a general need
• ongoing careful behavior
• not a single completed action

You are not being told to complete one action once; you are being told to stay careful in that situation.

That is why paziti fits well here.