المئزر مع صديقي.

Because Arabic often leaves out the present-tense verb to be.

So المئزر مع صديقي is a complete sentence in Arabic, even though it has no separate word for is. The meaning is understood as:

The apron is with my friend.

This is very common in Arabic nominal sentences. If you wanted the past, you would usually add a verb such as كان.

It is a full sentence.

Grammatically, it is a nominal sentence:

• المئزر = the topic/subject
• مع صديقي = the predicate/comment about it

So the sentence structure is basically:

[The apron] [with my friend]

which Arabic understands as The apron is with my friend.

الـ is the Arabic definite article, equivalent to the in English.

So:

• مئزر = an apron / apron
• المئزر = the apron

In this sentence, the noun is definite, which is very natural for the subject of a nominal sentence.

It is pronounced approximately al-miʾzar in pause, or al-miʾzaru with full case ending in careful pronunciation.

A few useful points:

• الـ = al-
• the م is a moon letter, so the l sound in al- is pronounced clearly
• ئ represents a hamza, so there is a slight catch in the voice: miʾ-

So it is not pronounced like the l disappears; you do say it: al-miʾzar.

مع means with.

In this sentence, it shows association or possession/location in the sense of:

• with my friend
• in my friend's possession
• together with my friend

So المئزر مع صديقي means the apron is currently with the friend, not necessarily that the apron and friend are doing something together in an active sense.

Because صديقي means my friend.

The ending ـي is a possessive suffix meaning my:

• صديق = friend
• صديقي = my friend

This is one of the most common ways Arabic shows possession. Instead of using a separate word for my, Arabic usually attaches it to the noun.

Because مع is followed by a noun in a genitive-type relationship, so صديق appears as صديقي here.

For a beginner, the easiest way to think of it is:

• مع = with
• after مع, the following noun takes the form expected after words like with

Since the noun also has the my suffix, the case ending is less obvious on the surface, but grammatically صديقي is the correct form here.

In fully vowelled, careful Arabic, you could analyze it like this:

• المِئْزَرُ = nominative, because it is the subject/topic of the nominal sentence
• صديقي = in the genitive relation after مع

In normal everyday writing, these short vowel endings are usually not written, so you just see:

المئزر مع صديقي

Arabic readers understand the grammar from context.

Yes, Arabic allows some flexibility, but المئزر مع صديقي is the most straightforward and neutral order for a learner.

This order gives:

• المئزر first as the thing being talked about
• مع صديقي after it as the comment

You may sometimes see prepositional phrases moved earlier for emphasis, but as a beginner, the given order is the safest pattern to use.

Because neither noun is indefinite in the way that takes tanwīn here.

• المئزر has الـ, so it is definite; definite nouns do not take tanwīn
• صديقي has the possessive suffix ـي meaning my, which also makes it definite, so it does not take tanwīn either

So the lack of tanwīn is exactly what you would expect.

Yes, depending on context, it can suggest:

• physical company: with my friend
• possession: held by my friend
• location in someone's keeping: with my friend

In this sentence, the most natural understanding is that the apron is in your friend's possession or is currently with him. Arabic often lets context decide the most precise shade of meaning.