הדירה בעיר גדולה, והיא חדשה.

In Hebrew, the verb to be is usually not written in the present tense in sentences like this.

So:

• הדירה גדולה = the apartment is big
• היא חדשה = it is new

Hebrew simply puts the subject and the adjective together, and the is is understood.

In past or future tense, Hebrew does use a form of to be, for example:

• הדירה הייתה גדולה = the apartment was big

The prefix ה- is the Hebrew definite article, meaning the.

So:

• דירה = apartment
• הדירה = the apartment

Unlike English, Hebrew usually does not use a separate word for the. It attaches it to the beginning of the noun.

Because דירה is a feminine singular noun, and Hebrew adjectives must agree with the noun they describe in:

• gender
• number

So:

• masculine singular: גדול, חדש
• feminine singular: גדולה, חדשה

Since דירה is feminine singular, the sentence uses גדולה and חדשה.

Yes, היא can mean she, but Hebrew also uses הוא / היא for it, depending on the grammatical gender of the noun.

Since דירה is feminine, Hebrew refers back to it with היא.

So here:

• והיא חדשה = and it is new

For a masculine noun, Hebrew would use הוא.

The prefix ו- means and.

Hebrew usually attaches this conjunction directly to the next word, instead of writing it as a separate word.

So:

• היא = she / it
• והיא = and she / and it

That is completely normal Hebrew spelling.

The ב- at the beginning means in, and Hebrew prepositions like ב-, ל-, and כ- are usually attached directly to the following word.

So:

• ב + עיר → בעיר

A tricky point: in ordinary unpointed Hebrew spelling, בעיר can represent either:

• be'ir = in a city
• ba'ir = in the city

The spelling is the same without vowel marks, so learners usually rely on:

• context
• pronunciation
• the given meaning

Because these adjectives are predicate adjectives, not attributive adjectives.

Compare:

• הדירה גדולה = the apartment is big
  Here גדולה is part of the statement, so it does not take ה-.

• הדירה הגדולה = the big apartment
  Here הגדולה directly modifies the noun, so it does take ה- to match the definite noun.

Same with חדשה:

• הדירה חדשה = the apartment is new
• הדירה החדשה = the new apartment

This is a very common and important distinction in Hebrew.

That is a very reasonable question, because at first glance עיר גדולה could mean big city.

In this sentence, though, the intended structure is:

• הדירה = the subject
• בעיר = a place phrase, in the city
• גדולה = the predicate adjective, is big

So the idea is:

• The apartment, in the city, is big

A learner may feel some temporary ambiguity while reading, especially because both דירה and עיר are feminine singular. Usually, context and the intended meaning make it clear.

Yes. That would also be natural Hebrew.

• הדירה בעיר גדולה וחדשה = The apartment in the city is big and new
• הדירה בעיר גדולה, והיא חדשה = The apartment in the city is big, and it is new

The version with והיא feels a little more like two separate linked statements, while the version without it is more compact.

Both are grammatical; the choice depends on style and emphasis.