Na okładce było zdjęcie kobiety, a w środku znalazłam zakładkę z adresem księgarni.

Because after na when it means on in a location sense, Polish uses the locative case.

• okładka = cover
• na okładce = on the cover

So okładce is the locative form of okładka.

A useful comparison:

• na okładce = on the cover
• na stole = on the table
• na zdjęciu = in/on the photo

W środku is a very common expression meaning inside or in the middle/interior.

Here it means inside the book or item being talked about.

Grammatically:

• w
  • locative is used for location
• środek = middle, interior
• w środku = inside / in the middle

So the sentence contrasts:

• na okładce = on the cover
• w środku = inside

Because zdjęcie is a neuter noun, and the past tense form of być must agree with it.

• masculine: był
• feminine: była
• neuter: było

Since zdjęcie is neuter, you say:

• było zdjęcie = there was a photo

This is very natural Polish word order for introducing something that existed somewhere.

Because Polish often uses the genitive case for of relationships.

• kobieta = woman
• kobiety = of a woman

So:

• zdjęcie kobiety = a photo of a woman

This is the same pattern as:

• adres księgarni = address of the bookstore
• okno domu = window of the house
• kolor samochodu = color of the car

Because the speaker is female.

In Polish past tense, the verb agrees with the gender of the person speaking:

• znalazłem = I found (said by a man)
• znalazłam = I found (said by a woman)

So this sentence tells you that the speaker is female.

Znalazłam is the perfective past form, from znaleźć, and it means I found as a completed action.

That fits the sentence because the speaker is talking about a single completed discovery:

• znalazłam zakładkę = I found a bookmark

The imperfective partner is znajdować, for example znajdowałam, but that would suggest an ongoing/repeated action and would sound wrong here in most contexts.

Here zakładka means bookmark.

It can also mean other things in other contexts, such as:

• a tab in a browser
• a tab in a file or document system

But because the sentence talks about the cover and inside, the book-related meaning bookmark is the natural one here.

Here z means with, and in that meaning it usually takes the instrumental case.

• adres = address
• adresem = with an address

So:

• zakładka z adresem księgarni = a bookmark with the bookstore’s address

Be careful: z can take different cases depending on meaning.

For example:

• z adresem = with an address → instrumental
• z Londynu = from London → genitive

Because this is another of relationship, so Polish uses the genitive.

• księgarnia = bookstore
• księgarni = of the bookstore

So:

• adres księgarni = the address of the bookstore

This is exactly the same pattern as:

• zdjęcie kobiety = photo of a woman

A often translates as and, but it is not exactly the same as i.

In many sentences, a links two ideas with a mild contrast or shift of focus:

• Na okładce było zdjęcie kobiety, a w środku... = There was a photo of a woman on the cover, and inside...

Here a helps move from one part of the object to another:

• on the cover ...
• inside ...

So it feels like and / while / whereas / and then on the other hand, depending on context.

Yes, Polish word order is flexible, and this sentence is arranged in a very natural information-flow way.

Current order:

• Na okładce było zdjęcie kobiety
  Literally: On the cover was a photo of a woman
• a w środku znalazłam zakładkę...
  and inside I found a bookmark...

This order emphasizes the location first:

• on the cover...
• inside...

You could also say things differently, for example:

• Zdjęcie kobiety było na okładce...

But that sounds a bit more like you are emphasizing the photo itself rather than introducing what was on the cover.

Yes. In this sentence, było zdjęcie works like an existential phrase: there was a photo.

Polish does not need a separate word like English there in this structure. It simply uses the verb plus the noun:

• Na okładce było zdjęcie kobiety
  = There was a photo of a woman on the cover

This kind of structure is very common in Polish.

This is a word many learners find tricky.

A rough guide is: ZDYEHN-cheh

Important points:

• zdj is pronounced together, not as separate English sounds
• ę before ci is often pronounced more like en/em in actual speech
• cie sounds roughly like cheh

So zdjęcie is approximately:

• zd-yen-cheh

Not a perfect English match, but that is a useful approximation.