بالکن آن آپارتمان کوچک بود، اما اتاق ها خیلی روشن بودند.

Persian usually links nouns with the ezafe sound -e instead of using a separate word like of.

So بالکن آن آپارتمان is read as bâlkon-e ân âpârtemân and means the balcony of that apartment.

A very important point: after a word ending in a consonant, this -e is usually not written, but it is still pronounced.

A simple transliteration is:

bâlkon-e ân âpârtemân kuchak bud, ammâ otâq-hâ kheyli roshan budand.

A few quick notes:

• kh in kheyli is the throaty sound in German Bach or Scottish loch
• â is a long a sound
• otâq-hâ means rooms

Because the verb agrees with the subject in number:

• بالکن = singular, so بود = was
• اتاق‌ها = plural, so بودند = were

So:

• بالکن ... کوچک بود = the balcony was small
• اتاق‌ها ... روشن بودند = the rooms were bright

Because Persian adjectives usually do not change for singular vs. plural.

So:

• اتاق روشن = bright room
• اتاق‌ها روشن = bright rooms

The adjective stays the same. The verb is what shows the plural here: بودند.

Yes, you will see that in everyday typing, but the more standard written form is:

اتاق‌ها

That uses a half-space (technically a zero-width non-joiner) before ها.

So:

• common informal typing: اتاق ها
• more standard typography: اتاق‌ها

Both mean exactly the same thing.

خیلی means very.

In Persian, words like very normally come before the adjective or adverb they modify:

• خیلی روشن = very bright
• خیلی کوچک = very small

So its position here is completely normal.

In Persian, the predicate usually comes before the form of to be.

So Persian naturally says something like:

• small was
• bright were

Even though in English we say:

• was small
• were bright

That is just a normal word-order difference between the two languages.

Here روشن means bright, light, or well-lit.

For a room, it usually suggests that the room has a lot of light, either from windows or lighting. It does not only mean that a lamp is switched on. It often describes how light and airy a space feels.

اما means but.

Yes, ولی can also mean but. In many situations they are interchangeable.

A simple way to think of them:

• اما = slightly more neutral or written
• ولی = often a bit more conversational

So this sentence could also use ولی and still sound natural.

Persian does not have a true definite article like English the.

That means a noun can often be understood as definite from context. In this sentence:

• آن آپارتمان explicitly means that apartment
• بالکن and اتاق‌ها are understood from the context

If Persian wants to emphasize a/an, it often uses یک, but it is not always necessary.

Because the sentence structure is:

[subject] + [predicate adjective] + [verb]

Here the subject is بالکنِ آن آپارتمان = the balcony of that apartment, and کوچک بود means was small.

If you wanted that small apartment, Persian would need an ezafe relationship after آپارتمان as well:

آن آپارتمانِ کوچک

In normal Persian spelling, ezafe is often not written, so sometimes the reader relies on context and sentence structure to understand it.