انا اجلس على الكرسي قرب النافذة، ثم أقرأ البريد الإلكتروني.

Yes. In Modern Standard Arabic, the verb أجلس already tells you the subject is I.

So:

• أجلس = I sit / I am sitting
• أنا أجلس = I sit / I am sitting, with the pronoun made explicit

Including أنا can add:

• emphasis
• clarity
• a slightly more deliberate tone

In many cases, Arabic can drop the subject pronoun because the verb already contains that information.

أجلس is a present-tense (more precisely, imperfect) verb in the first person singular.

It comes from the verb جلس = to sit

Its present-tense forms include:

• أجلس = I sit / I am sitting
• تجلس = you sit / she sits
• يجلس = he sits
• نجلس = we sit

The prefix أ- is what marks the I form in the present tense.

It can mean either one, depending on context.

In MSA, the present tense often covers both:

• simple present: I sit
• present progressive: I am sitting

So أنا أجلس على الكرسي could mean:

• I sit on the chair
• I am sitting on the chair

The surrounding context tells you which is more natural.

على means on, upon, or sometimes on top of.

With the verb جلس (to sit), Arabic commonly uses على:

• جلس على الكرسي = he sat on the chair
• أجلس على الكرسي = I sit / am sitting on the chair

This is just the normal Arabic pattern. English learners sometimes wonder whether Arabic would use something like in or at, but على is the standard choice here.

Yes—formally, after a preposition like على, the noun is in the genitive case.

So in fully vocalized MSA, you would write:

• على الكرسيِّ

The final -i sound marks the genitive case.

However, in normal everyday Arabic writing, short vowel endings are usually not written, so you commonly just see:

• على الكرسي

That is completely normal.

قرب means near.

It often behaves like a preposition-like word or an adverbial noun meaning nearby / near.

So:

• قرب النافذة = near the window

In full formal grammar, this phrase is often analyzed as:

• قربَ = an adverbial expression meaning near
• النافذةِ = a noun in the genitive after it

So the fully vocalized form is often:

• قربَ النافذةِ

For a learner, the easiest practical takeaway is:

• قرب + noun = near + noun

You may also see another common way to say this idea:

• قريبًا من النافذة
• بالقرب من النافذة

But قرب النافذة is perfectly good and concise MSA.

This is because ن is a sun letter.

In Arabic, the ل in الـ is pronounced clearly before moon letters, but it is assimilated before sun letters.

So:

• الكرسي → al-kursī because ك is a moon letter
• النافذة → pronounced an-nāfiḏa because ن is a sun letter

In writing, it still stays النافذة, but in pronunciation the l sound disappears and the n sound is doubled.

ثم means then or after that.

It shows sequence: one action happens, and then the next one happens.

So:

• أنا أجلس على الكرسي قرب النافذة، ثم أقرأ البريد الإلكتروني. = I sit on the chair near the window, then I read the email.

If you used و instead, it would simply mean and, without emphasizing the order as clearly:

• ... وأقرأ ... = ... and I read ...

So ثم is a better choice when you want first this, then that.

أقرأ is from the verb قرأ = to read.

It is pronounced approximately:

• ʾaqraʾu

Important points:

• the first أ is the present-tense prefix for I
• the final ء is a real consonant called hamza
• it does not just disappear in careful pronunciation

So أقرأ is not simply aqraa. The ending includes a glottal stop:

• aqraʾ

This happens because the root itself contains hamza: ق ر أ

No, this is not an iḍāfa.

It is:

• البريد = the mail / the post
• الإلكتروني = electronic

So this is a noun + adjective structure:

• البريد الإلكتروني = the electronic mail = email

A good clue is that both words have ال.

In an iḍāfa, usually only the first noun is bare and the second noun carries the definiteness, for example:

• بابُ البيتِ = the door of the house

But here, الإلكتروني is an adjective describing البريد, so it agrees with it in:

• definiteness
• gender
• number
• case

Because Arabic adjectives agree with the nouns they describe.

Here:

• البريد is masculine
• singular
• definite

So the adjective must also be:

• masculine
• singular
• definite

That gives:

• البريد الإلكتروني

If the noun changed, the adjective would change too.

This agreement is a very important feature of Arabic grammar.

A fully vocalized version would be:

أَنا أَجْلِسُ عَلَى الكُرْسِيِّ قُرْبَ النَّافِذَةِ، ثُمَّ أَقْرَأُ البَرِيدَ الإِلِكْتُرُونِيَّ.

Some useful things to notice:

• أجلسُ and أقرأُ end in -u because they are present-tense verbs in the normal indicative form
• الكرسيِّ is genitive after على
• النافذةِ is genitive after قرب
• البريدَ is accusative because it is the direct object of أقرأ
• الإلكترونيَّ matches البريدَ in case, definiteness, gender, and number

In ordinary writing, these short vowels are usually omitted.

Yes. A very natural version is:

أجلس على الكرسي قرب النافذة، ثم أقرأ البريد الإلكتروني.

This is often how Arabic is written and spoken, since the verb already tells you the subject is I.

So both are correct:

• أنا أجلس ...
• أجلس ...

The version with أنا is a bit more explicit or emphatic.