Když mám hlad, dám si teplou polévku.

Here když mainly means when or whenever.

So Když mám hlad... means When I’m hungry... or Whenever I’m hungry...

In everyday Czech, když can sometimes overlap a bit with if, but the basic meaning is when. If you want a more clearly conditional if, Czech often uses jestli or pokud.

Czech normally uses the expression mít hlad, literally to have hunger.

So:

• mám hlad = I’m hungry
• máš hlad = you’re hungry
• mají hlad = they’re hungry

This is the most common everyday way to say it.

You can also hear jsem hladový / hladová, but that is less neutral in simple everyday speech.

It is in the accusative, because mít takes a direct object here: mít hlad.

The tricky part is that hlad is a masculine inanimate noun, and in the singular its nominative and accusative look the same:

• nominative: hlad
• accusative: hlad

So the form does not change, even though the case does.

Dám si comes from dát si.

Literally, dát means to give, and dát si is literally something like to give to oneself. But with food and drink, it very often means:

• to have
• to eat
• to drink
• to get for oneself

So dám si teplou polévku means something like:

• I’ll have some hot soup
• I’ll get myself some hot soup
• I’ll eat some hot soup

Si is a short reflexive pronoun, here meaning roughly for myself.

In dát si, it is an important part of the expression. With food and drink, it helps create the meaning to have/eat/drink something.

If you leave it out, the meaning changes:

• dám si polévku = I’ll have some soup
• dám polévku = I’ll give the soup

So in this sentence, si should not be omitted.

This is about aspect.

• dát si is perfective
• dávat si is imperfective

Dám si focuses on one complete action: I’ll have some soup.

That is why it can sound a bit future-like in English, even though the form looks present. Perfective present forms in Czech often refer to a future completed action.

So this sentence can feel like:

• When I’m hungry, I’ll have some hot soup
• or more generally, When I’m hungry, I have some hot soup

If you wanted to stress a repeated habit more clearly, dávám si could also appear in other contexts.

Because it is the direct object of dám si, so it goes into the accusative.

Dictionary form:

• teplá polévka = hot/warm soup

Accusative form:

• teplou polévku

Both words change because polévka is feminine singular:

• teplá → teplou
• polévka → polévku

Usually teplý means warm or hot in a general, non-extreme way.

For something very hot, Czech often uses horký.

So:

• teplá polévka = warm/hot soup
• horká polévka = very hot, piping-hot soup

In everyday use, teplá polévka is completely natural.

Because Když mám hlad is a subordinate clause, and Czech normally separates subordinate clauses with a comma.

So:

• Když mám hlad, dám si teplou polévku.

If you reverse the order, you still use a comma:

• Dám si teplou polévku, když mám hlad.

Czech is generally stricter about this than English.

Yes. Czech word order is fairly flexible.

For example:

• Když mám hlad, dám si teplou polévku.
• Dám si teplou polévku, když mám hlad.

Both are grammatical. The main difference is emphasis:

• starting with Když mám hlad highlights the situation first
• starting with Dám si teplou polévku highlights the action first

The original order is very natural.

Because Czech does not have articles.

So polévku by itself can mean different things depending on context, such as:

• soup
• the soup
• some soup
• sometimes even a soup

In natural English, this sentence is often best understood as something like some hot soup or a bowl of hot soup, but Czech does not need a separate word for that.