في المساء أكتب رسالة لصديقي من هاتفي.

في المساء means in the evening.

• في = in
• المساء = the evening

Arabic often uses في with time expressions, especially when English would use in or sometimes at. So:

• في الصباح = in the morning
• في المساء = in the evening
• في الليل = at night / in the night

The ال on المساء is the definite article the, so literally it is in the evening.

Arabic is flexible with word order, and starting with في المساء puts the time first for emphasis or natural flow.

So:

• في المساء أكتب رسالة لصديقي من هاتفي. = In the evening, I write a message to my friend from my phone.

If you changed the order to:

• أكتب رسالة لصديقي من هاتفي في المساء

that would also be correct, but it sounds more like I write a message to my friend from my phone in the evening, with the action first and the time added later.

Putting the time phrase first is very common in Arabic.

The subject I is built into the verb أكتب.

• أكتب = I write / I am writing

In Arabic, verbs usually already show the subject, so a separate pronoun like أنا is often unnecessary.

• أكتب = I write
• تكتب = you write or she writes depending on context
• يكتب = he writes
• نكتب = we write

You could say أنا أكتب for extra emphasis, but normally just أكتب is enough.

أكتب is the present/imperfect form.

In Arabic, this form can cover several meanings that English separates:

• I write
• I am writing
• I do write
• sometimes even I will write, depending on context

In this sentence, the most natural translation is probably either:

• In the evening, I write a message to my friend from my phone
• In the evening, I am writing a message to my friend from my phone

Context tells you whether it is habitual or happening right now. On its own, Arabic does not always force that distinction.

Arabic has no separate word for a or an.

Instead:

• a noun without ال is usually indefinite
• a noun with ال is usually definite

So:

• رسالة = a message / a letter
• الرسالة = the message / the letter

In fully vowelled Arabic, the indefinite form would often appear as رسالةً in this sentence, but short vowels are usually not written in normal Arabic text.

It can mean either, depending on context.

• رسالة can be letter
• رسالة can also be message

Because the sentence includes من هاتفي (from my phone), many learners would understand it as message in modern everyday usage. But grammatically, رسالة itself can mean both.

The لـ here means to or for.

So:

• لصديقي = to my friend

This is made of:

• لِـ = to / for
• صديقي = my friend

Because لِـ is attached directly to the next word, you see them written together:

• لِ + صديقي = لصديقي

This is very common in Arabic. Other examples:

• للمعلم = to the teacher
• لكتابي = for my book or to my book depending on context

صديقي is:

• صديق = friend
• ـي = my

So:

• صديقي = my friend

This ـي is a possessive suffix. Arabic often shows possession by attaching a pronoun directly to the noun.

Examples:

• كتابي = my book
• بيتي = my house
• هاتفي = my phone

Also notice that when a noun takes a possessive suffix, it is already definite, so you do not add ال. That is why صديقي is correct, not الصديقي.

Yes. من usually means from, but in context it can also suggest the source or medium.

So من هاتفي literally means from my phone, and in natural English it may be understood as:

• from my phone
• on my phone
• using my phone

This is one of those places where Arabic and English do not match word-for-word perfectly. Arabic uses من naturally here to show that the phone is the means or source of sending/writing the message.

A helpful pronunciation guide is:

• لصديقي = li-ṣa-dii-qii
• هاتفي = haa-ti-fii

A few details:

• ص is an emphatic s, deeper than ordinary س
• ديق in صديق has a long ii sound: ṣadīq
• the final ـي in صديقي and هاتفي is a long ee sound meaning my

So the whole phrase sounds roughly like:

• li-ṣadīqī min hātifī

A fully vowelled version would be:

في المساءِ أكتبُ رسالةً لصديقي من هاتفي.

Here is what the endings show:

• المساءِ after في takes genitive case
• أكتبُ has the normal indicative ending ـُ
• رسالةً is indefinite and is the direct object
• صديقي and هاتفي already include my, so they do not need ال

In everyday Arabic writing, these short vowels are usually omitted, so you normally see:

في المساء أكتب رسالة لصديقي من هاتفي

Yes. The verb form أكتب can describe either:

• a current action: I am writing
• a regular/habitual action: I write

So the sentence can naturally be understood as:

• In the evening, I am writing a message to my friend from my phone
• In the evening, I write a message to my friend from my phone

If you wanted to make the habitual meaning clearer, context would usually do that. Arabic often relies more on context than English does for this distinction.