صديقي يجلب زجاجة عصير.

The base word is صديق = friend. The ending ـي is the attached pronoun meaning my.

So:

• صديق = friend
• صديقي = my friend

This ending is very common in Arabic:

• كتابي = my book
• بيتي = my house

Because a noun with a possessive ending is already definite.

So صديقي already means my friend, which is definite. Arabic does not add ال to a noun that already has a suffix like ـي.

So الصديقي would be incorrect in MSA.

يجلب is a present/imperfect-tense verb meaning he brings or he is bringing, depending on context.

Its form here is:

• يـ = third person masculine singular
• جلب = the root idea of bringing

So يجلب matches صديقي because صديقي is masculine singular.

Because the subject صديقي is masculine singular.

In the present tense:

• يجلب = he brings
• تجلب = she brings / you bring, depending on context

If the sentence were صديقتي تجلب زجاجة عصير, it would mean my female friend brings a bottle of juice.

Because the verb already contains that information.

يجلب already tells you the subject is he. Since the sentence also explicitly says صديقي, there is no need to add a separate pronoun.

Arabic often works this way: the verb itself includes person, number, and gender.

Both orders are possible in MSA.

• صديقي يجلب زجاجة عصير
• يجلب صديقي زجاجة عصير

Both are grammatical. The first is a subject–verb order, which is very common in Modern Standard Arabic, especially in straightforward modern prose. The second is a more traditional verb–subject order.

In this sentence, the meaning stays essentially the same.

Arabic has no separate indefinite article like a or an.

So a bare indefinite noun can often be translated with a/an in English.

• زجاجة = a bottle
• الزجاجة = the bottle

That is why زجاجة can naturally mean a bottle.

Yes. This is an iḍāfa construction, often called the construct phrase.

Arabic usually expresses X of Y by putting two nouns next to each other:

• زجاجة عصير = bottle of juice
• باب البيت = door of the house
• كتاب الطالب = the student’s book

So Arabic does not need a separate word like of here.

Because it is the first word of an iḍāfa.

The first noun in an iḍāfa:

• does not take ال
• does not take tanwīn

So in full case endings, this would be:

• زجاجةَ عصيرٍ

not

• زجاجةً عصيرٍ

It is still indefinite in meaning here, but tanwīn disappears because of the construct structure.

Because the whole phrase is indefinite: a bottle of juice.

In an iḍāfa, the definiteness of the whole phrase is determined by the second noun:

• زجاجةُ عصيرٍ = a bottle of juice
• زجاجةُ العصيرِ = the bottle of the juice / the juice bottle, depending on context

So عصير is indefinite here, which matches the English meaning a bottle of juice.

When ة appears at the end of a word in pause, it is usually pronounced like -a or -ah.

But when the word is connected grammatically, especially in an iḍāfa, the ة is pronounced as t.

So here, زجاجة عصير is pronounced more like:

zujājat ʿaṣīr

rather than just zujāja.

That is a very common pattern in Arabic.

A fully vowelled version would be:

صَديقي يَجْلِبُ زُجاجَةَ عَصيرٍ

Here is what is happening:

• صديقي = the subject, grammatically nominative, but the case ending is not visible because of the ـي suffix
• يجلبُ = present tense verb in the indicative
• زجاجةَ = direct object, so accusative
• عصيرٍ = genitive because it is the second noun in the iḍāfa

So even though learners may not always write the endings, the grammar behind them is still there.

It can mean either one, depending on context.

The Arabic imperfect often covers both:

• he brings
• he is bringing

If you want to make right now especially clear, Arabic often relies on context or adds a word such as الآن = now.

So:

• صديقي يجلب زجاجة عصير الآن = my friend is bringing a bottle of juice now