لو كانت عندي شرفة أكبر، لوضعت فيها طاولة وكرسيا.

This is a hypothetical / counterfactual conditional.

With لو, Arabic often expresses an unreal situation, like:

لو كانت عندي شرفة أكبر، لوضعت فيها طاولة وكرسيا
= If I had a bigger balcony, I would put a table and a chair in it.

So the speaker does not have a bigger balcony in reality; this is just imagining what would happen if they did.

Because Arabic commonly uses the past tense form in both parts of a counterfactual لو sentence.

So:

• كانت literally looks like was
• وضعت literally looks like I put

But with لو, the whole pattern means something like:

• if I had...
• I would put...

This is very normal in Arabic. The past form here does not mean simple past time.

Because شرفة is a feminine singular noun, and كان agrees with it:

• كان = masculine singular
• كانت = feminine singular

So:

• شرفة = balcony, feminine
• therefore كانت

No. Here لوضعت is not the conditional particle لو again.

It is best understood as:

لَ + وضعتُ → لَوَضَعْتُ

This لَـ is the lām often used in the result clause after لو. It adds the sense of then I would...

So the pronunciation is:

• first لو = law
• لوضعت here = la-waḍaʿtu, not law waḍaʿtu

That is an important distinction.

Arabic often expresses possession with a phrase meaning at me / with me, rather than a verb exactly like English have.

• عندي = at me / with me
• so كانت عندي شرفة literally means something like there was, at me, a balcony
• natural English: I had a balcony

This is a very common Arabic way to express possession.

In grammatical terms:

• عندي is the predicate of كان (خبر كان) placed first
• شرفة is the noun of كان (اسم كان) placed later

So the structure is roughly:

• كانت = was
• عندي = with me / at me
• شرفة = a balcony

A fully vocalized form would be:

لَوْ كانَتْ عِنْدي شُرْفَةٌ أَكْبَرُ

Here شرفةٌ is nominative because it is the اسم كان.

Because أكبر here is a regular comparative meaning bigger.

In ordinary comparison, Arabic usually uses the أفعل form:

• أكبر = bigger / أكبر

So:

• شرفة أكبر = a bigger balcony

The form كبرى does exist, but it is more often used in certain fixed expressions, titles, or superlative-like uses, such as القضية الكبرى or الشرفة الكبرى in a more specific context. For a simple everyday comparative like a bigger balcony, شرفة أكبر is the normal choice.

Because أكبر is on the أفعل pattern, and words of this type are usually diptotes.

That means they do not take tanwīn.

So you get:

• شرفةٌ أكبرُ
• not شرفةٌ أكبرٌ

This is normal for many comparative/superlative forms like أكبر، أصغر، أحسن، أفضل.

فيها = في + ها

• في = in
• ها = her / it (feminine singular)

Since شرفة is feminine, ها refers back to it.

So فيها means:

• in it
• more literally: in her, but in English we say in it

Here it means in the balcony.

Because they are the direct objects of وضعتُ:

• وضعتُ طاولةً = I would put a table
• وكرسيًّا = and a chair

So in full vocalization:

طاولةً وكرسيًّا

In ordinary unvocalized writing, those endings are usually not shown, so you may simply see:

طاولة وكرسيا

In fully vocalized Arabic, this word would be:

كُرْسِيًّا

But in normal writing, short vowels and shadda are often omitted, so it can appear as:

كرسيا

So this spelling is just the unvocalized written form of the accusative indefinite كرسيًّا.

Yes. That would also be correct:

لو كانت لدي شرفة أكبر، لوضعت فيها طاولة وكرسيا.

Both are acceptable in Modern Standard Arabic.

Very roughly:

• عندي is common and natural
• لدي is often felt to be a bit more formal or written

A fully vocalized version is:

لَوْ كانَتْ عِندي شُرْفَةٌ أَكْبَرُ، لَوَضَعْتُ فيها طاوِلَةً وَكُرْسِيًّا.

Approximate pronunciation:

law kānat ʿindī shurfatun akbaru, lawaḍaʿtu fīhā ṭāwilatan wa-kursiyyan

A few important points in pronunciation:

• first لو = law
• لوضعت = la-waḍaʿtu
• فيها = fīhā
• أكبر = akbaru