Na końcu ulicy jest apteka.

Because na końcu uses the locative case after na to express a location: where something is.

• na końcu = at the end
• na koniec usually means for the end / at the end (as a final point) and is not used here for physical location

So in this sentence, since the pharmacy is located somewhere, Polish uses na + locative:

• na końcu ulicy = at the end of the street

Because ulicy is in the genitive singular.

The noun koniec often takes another noun in the genitive, just like English the end of the street:

• koniec ulicy = the end of the street

Here:

• base form: ulica = street
• genitive singular: ulicy

So the structure is:

• na końcu = at the end
• ulicy = of the street

Because after na in a location phrase, Polish normally uses the locative case.

The dictionary form is:

• koniec = end

But in this sentence it becomes:

• na końcu = at the end

So:

• koniec = nominative
• końcu = locative singular

This is a very common pattern in Polish:

• w domu = in the house
• na stole = on the table
• na końcu = at the end

Here jest means is, but in this kind of sentence it works like there is in English.

So structurally, Polish says something like:

• At the end of the street is a pharmacy

In natural English, that often becomes:

• There is a pharmacy at the end of the street

So jest is the verb to be, 3rd person singular:

• jest = is

Usually in the present tense, Polish often omits forms of to be when linking a subject and a description:

• On jest lekarzem often becomes On lekarzem in some contexts? Actually with professions in modern standard Polish, jest is usually kept.

But in existence/location sentences like this one, jest is normally not omitted:

• Na końcu ulicy jest apteka. = correct
• leaving out jest here would sound incomplete or unnatural

So in this sentence, jest is important.

Because apteka is the grammatical subject of the sentence, and in this kind of statement the subject is in the nominative case.

• apteka = nominative singular
• dictionary form: apteka

Even though English uses there is, Polish still keeps the thing that exists in the nominative:

• Jest apteka
• Jest sklep
• Jest bank

So apteka stays in its basic form.

No, Polish word order is fairly flexible.

This sentence:

• Na końcu ulicy jest apteka.

could also be:

• Apteka jest na końcu ulicy.

Both are correct, but the emphasis changes a little.

• Na końcu ulicy jest apteka.
  starts with the location, so it feels like At the end of the street, there is a pharmacy.
• Apteka jest na końcu ulicy.
  starts with pharmacy, so it feels more like The pharmacy is at the end of the street.

The original version is very natural if you are introducing what is in that place.

Because Polish has no articles like a / an / the.

So:

• apteka can mean a pharmacy or the pharmacy
• ulica / ulicy can mean street / the street, depending on context

Polish relies on context, word order, and sometimes extra words like:

• ta apteka = this pharmacy
• ta ulica = this street

In your sentence, English may need a or the, but Polish does not.

This is a very common learner question because they look similar, but they mean different things.

• na końcu = at the end in a physical or ordered sense

  • na końcu ulicy = at the end of the street
  • na końcu listy = at the end of the list

• w końcu usually means finally / eventually / after all

  • W końcu przyszedł. = He finally came.
  • W końcu to twoja decyzja. = After all, it’s your decision.

So in this sentence, only na końcu works.

A rough pronunciation guide is:

• Na → nah
• końcu → roughly KOIN-tsoo
  
  • ń is a soft n sound
  • c in Polish is pronounced like ts
• ulicy → roughly oo-LEE-tsih
• jest → roughly yest
• apteka → roughly ap-TEH-ka

A fuller rough version:

• nah KOIN-tsoo oo-LEE-tsih yest ap-TEH-ka

Stress in Polish is usually on the second-to-last syllable:

• końcu
• ulicy
• apteka

Yes, very natural.

It is a standard way to describe something located at the far end of a street.

Similar natural phrases include:

• na końcu drogi = at the end of the road
• na końcu korytarza = at the end of the corridor
• na końcu miasta = at the edge/end of the town, depending on context

If you want to be more specific, you could also say:

• Na końcu tej ulicy jest apteka. = There is a pharmacy at the end of this street.

Usually na końcu ulicy is the more natural choice for at the end of the street.

• na końcu ulicy strongly suggests the pharmacy is located right at the end
• przy końcu ulicy would sound more like near the end of the street, and is less standard in many contexts

So if you mean the exact or normal idea of at the end of the street, use:

• na końcu ulicy

By itself, it can be understood either way depending on context.

• Na końcu ulicy jest apteka. often introduces new information: There is a pharmacy at the end of the street.
• If the pharmacy is already known, Polish could still use the same sentence, or use a different word order:
  • Apteka jest na końcu ulicy.

Because Polish has no articles, context tells you whether English should use a or the.