Nauczycielka pokazuje, gdzie wstawić przecinek, a gdzie postawić kropkę.

Nauczycielka means female teacher, while nauczyciel means male teacher.

Polish often marks the teacher’s gender directly in the noun:

• nauczyciel = male teacher
• nauczycielka = female teacher

So this sentence specifically tells us that the teacher is a woman.

Polish usually does not need subject pronouns like he, she, or it if the verb already makes the subject clear.

Here, pokazuje means shows / is showing, and the subject is already given by nauczycielka, so adding ona would be unnecessary:

• Nauczycielka pokazuje... = The teacher shows...
• Ona pokazuje... would mean She shows..., but it is not needed here.

Polish is a pro-drop language, so leaving out subject pronouns is very normal.

Pokazuje is the 3rd person singular present tense form of pokazywać.

So it means:

• he/she/it shows
• or, depending on context, is showing

Because the subject is nauczycielka, here it means:

• the female teacher shows

Aspect is also important:

• pokazywać = imperfective
• it describes an ongoing, repeated, or general action

So the sentence presents the action as a normal act of explaining or demonstrating, not as a one-time completed action.

Because gdzie wstawić przecinek is a subordinate clause.

In Polish, subordinate clauses are usually separated by commas. So:

• Nauczycielka pokazuje, gdzie wstawić przecinek...

Literally, this is something like:

• The teacher shows where to put a comma...

The part beginning with gdzie functions like where to..., and Polish requires a comma before that clause.

It is used twice because there are two parallel clauses:

• gdzie wstawić przecinek
• a gdzie postawić kropkę

This structure means:

• where to insert a comma
• and where to put a period

Repeating gdzie makes the parallel structure clear and natural in Polish. English often does the same:

• where to put a comma and where to put a period

In this sentence, a works better because it links two contrasted or paired pieces of information:

• where to put a comma
• and where to put a period

Polish a often means something like:

• and
• while
• whereas
• or a gentle contrast between two items

Here it is not a strong opposition, but it does set up a contrast between one place and another place / one punctuation mark and another.

If you used i, it would sound more like a simple addition. A is more natural in this kind of paired structure.

This is mainly about natural collocation in Polish.

Polish commonly says:

• wstawić przecinek = to insert a comma
• postawić kropkę = to put a period / full stop

The verbs are both understandable literally:

• wstawić = to insert, put in
• postawić = to place, put

But with punctuation, certain combinations are just more idiomatic. English does this too:

• we say make a decision, not usually do a decision
• we say put a comma, not build a comma

So this sentence sounds natural because it uses common Polish verb-noun pairings.

Both words are actually direct objects, so both are in the accusative case. The reason they look different is that different nouns change differently.

• przecinek is a masculine inanimate noun
• kropka is a feminine noun

In the singular:

• many masculine inanimate nouns have the same form in nominative and accusative
• many feminine nouns ending in -a change that -a to -ę in the accusative

So:

• przecinek → przecinek
• kropka → kropkę

That is why only the second one visibly changes.

Both verbs take a direct object in the accusative case.

So:

• wstawić przecinek → przecinek is accusative
• postawić kropkę → kropkę is accusative

This matches the basic pattern:

• verb + object

For example:

• wstawić zdjęcie = to insert a photo
• postawić szklankę = to put down a glass

In your sentence, the objects are punctuation marks.

Because they depend on gdzie in a structure that means where to do something.

So:

• gdzie wstawić przecinek = where to insert a comma
• gdzie postawić kropkę = where to put a period

This is very similar to English where to + verb.

The teacher is showing:

• where to insert
• where to put

So the infinitive is exactly what you would expect after this kind of expression.

Both wstawić and postawić are perfective verbs.

That makes sense because the actions are treated as single completed acts:

• you insert a comma at a particular point
• you put a period at a particular point

Perfective verbs often fit well when talking about a finished result:

• the comma gets inserted
• the period gets placed

Their imperfective partners would be:

• wstawiać
• stawiać

But here the sentence is not about the ongoing process of punctuation in general. It is about showing the correct spot for a completed action, so the perfective infinitives are natural.

Yes, Polish word order is fairly flexible, although the original version is the most natural and neutral.

Original:

• Nauczycielka pokazuje, gdzie wstawić przecinek, a gdzie postawić kropkę.

You could sometimes rearrange parts for emphasis, but not every version sounds equally natural. The given sentence is good because it is:

• clear
• balanced
• idiomatic

In particular, the parallel structure

• gdzie wstawić..., a gdzie postawić... sounds very smooth.

Here gdzie means where, but in context it really means:

• in which place
• at what point in the text

So the sentence is not about physical location in a room. It is about the correct position in writing for punctuation marks.

That is very natural in both Polish and English:

• where to put a comma
• where to put a period

So gdzie is simple, but the context tells you it means where in the sentence/text.