بعد العشاء أقرأ كتابا في الغرفة.

Because the verb itself already shows the subject.

• أقرأُ means I read / I am reading
• The prefix أ- on the verb tells you the subject is I

So أنا أقرأُ is possible, but أنا is usually unnecessary unless you want emphasis, contrast, or clarity.

• أقرأُ كتابًا = I read a book
• أنا أقرأُ كتابًا = I am the one reading a book / I read a book

أقرأُ is in the Arabic imperfect (non-past) form. In English, that can correspond to different ideas depending on context:

• I read
• I am reading
• I will read

In this sentence, with بعد العشاء (after dinner), the most natural interpretation is something like:

• I read a book after dinner
• or After dinner, I read/am reading a book

If you wanted a clearly future meaning in MSA, you could add سـ or سوف:

• سأقرأُ كتابًا = I will read a book

Because it is an indefinite direct object, so it takes the accusative ending.

Here:

• أقرأُ = I read
• كتابًا = a book

Since book is the thing being read, it is the direct object, so in full MSA it takes fatḥatayn (tanwīn fatḥ): كتابًا.

A very common pattern is:

• أكتبُ رسالةً = I write a letter
• أقرأُ كتابًا = I read a book

In everyday pronunciation, especially in pause, learners may not always hear the full case ending clearly, but in formal MSA grammar it is there.

Because the sentence means a book, not the book.

• كتابًا = a book
• الكتابَ = the book

So:

• أقرأُ كتابًا = I read a book
• أقرأُ الكتابَ = I read the book

Arabic does not have a separate word for a/an. Indefiniteness is usually shown by the lack of الـ and, in fully vowelled MSA, often by tanwīn.

Because it comes after بعدَ in an iḍāfa-like construction: بعدَ العشاءِ = after dinner.

In standard grammar:

• بعدَ is often treated as a ظرف (adverbial noun) in the accusative
• the noun after it is in the genitive, so you get العشاءِ

So the fully vowelled phrase is:

• بعدَ العشاءِ

This is similar to other time expressions built the same way.

Because it comes after the preposition في (in).

In Arabic, a noun after a preposition is normally genitive, so:

• في الغرفةِ = in the room

Compare:

• في البيتِ = in the house
• في المدرسةِ = in the school

So the -i ending here is caused by في.

Arabic word order is more flexible than English word order.

Starting with بعد العشاء puts the time expression first:

• بعد العشاء أقرأ كتابًا في الغرفة = After dinner, I read a book in the room

This is very natural in Arabic. You could also say:

• أقرأُ كتابًا في الغرفةِ بعدَ العشاءِ

That would still be correct, but the emphasis/focus would be slightly different. Putting بعد العشاء first highlights the time.

Yes, often you can.

For example, these are all possible with roughly the same core meaning:

• بعدَ العشاءِ أقرأُ كتابًا في الغرفةِ
• أقرأُ كتابًا في الغرفةِ بعدَ العشاءِ
• في الغرفةِ أقرأُ كتابًا بعدَ العشاءِ

The differences are mainly about focus and style, not the basic meaning.

Arabic uses word order more freely than English, especially with adverbial phrases like time and place.

Because الغرفة means the room, while غرفة means a room.

• في الغرفةِ = in the room
• في غرفةٍ = in a room

So the sentence as written refers to a specific room, or at least a room understood from context.

A few sounds here are especially important:

• ع in العشاء is a deep throat sound with no exact English equivalent
• غ in الغرفة is like a voiced, gargled r / French-like r
• ش is like English sh

A rough learner-friendly pronunciation:

• العشاء ≈ al-ʿishāʾ
• الغرفة ≈ al-ghurfah

Also note:

• In الغرفة, the l of ال is pronounced, because غ is a moon letter
• So it is al-ghurfah, not agh-ghurfah

Here it means dinner / supper / the evening meal.

In other contexts, العشاء can also refer to the ʿIshāʾ prayer in Islamic usage. But in this sentence, since the meaning is already given and the context is everyday routine, it is understood as dinner.

In careful, formal MSA, yes, they are part of the grammar:

• بعدَ
• العشاءِ
• أقرأُ
• كتابًا
• في الغرفةِ

But in actual reading aloud and especially in pause, final short vowels are often reduced or not fully pronounced. In less formal speech, many speakers also simplify case endings a lot.

So for learning purposes:

• It is good to know the case endings
• But you should also expect to hear less than the full system in real usage

The sentence is:

• بعدَ العشاءِ = time expression, after dinner
• أقرأُ = verb, I read / I am reading
• كتابًا = direct object, a book
• في الغرفةِ = place expression, in the room

So the structure is basically:

time + verb + object + place

That is a very common and natural pattern in Arabic.