اختي عارفة تكتب على الكمبيوتر.

A natural Egyptian pronunciation is:

okhti ʿārfa tiktib ʿala l-kombyūter

A few sound notes:

• خ is the rough kh sound, like the ch in German Bach
• ع is the consonant ʿayn, a sound English does not really have
• الكمبيوتر is a loanword and is commonly pronounced something like el-kombyūter

اختي means my sister.

It is made of:

• أخت / اخت = sister
• -ي = my

So the -ي is a possessive suffix. Arabic often attaches possessive endings directly to the noun instead of using a separate word for my.

The more careful spelling is أختي with a hamza on the alif.

In informal writing, especially in Egyptian Arabic, people often leave the hamza off and write اختي instead. So:

• أختي = more standard spelling
• اختي = very common casual spelling

They mean the same thing.

In Arabic, the present-tense is/am/are is usually not said.

So اختي عارفة literally looks like my sister knowing, but it means my sister is knowledgeable / knows.

This is a very normal Arabic structure:

• اختي = the subject
• عارفة تكتب على الكمبيوتر = the predicate

If you wanted past or future, you would usually need extra words, but in the present this zero-copula structure is standard.

Because اختي is feminine.

In Arabic, words like عارف / عارفة agree with the person they describe:

• عارف = masculine
• عارفة = feminine

Since my sister is feminine, you use عارفة.

Here عارفة تكتب means knows how to write or can write/type.

In Egyptian Arabic, عارف / عارفة + verb is very commonly used for learned ability or familiarity:

• أنا عارف أسبح = I know how to swim
• هي عارفة تسوق = She knows how to drive

So in this sentence, عارفة تكتب is best understood as knows how to write / can write.

Arabic does not use an infinitive the same way English does.

English says:

• to write

But Arabic usually uses a finite verb form instead. So:

• عارفة تكتب literally resembles knowing she-writes
• but the real meaning is knows how to write

This is a normal Arabic pattern. You do not need a separate word equal to English to here.

Yes. In Arabic, تكتب can match more than one subject depending on context.

It can mean:

• she writes
• you write to one masculine person

In this sentence, the context makes it clear that it belongs with اختي and means she writes / she can write.

That kind of overlap is very common in Arabic verb forms.

By itself, تكتب usually means write.

But with على الكمبيوتر, it will often be understood as type or write on a computer.

So in context, the sentence can naturally mean:

• My sister knows how to write on the computer
• My sister knows how to type

If you want to be very specific, context usually does the job.

على literally means on.

So على الكمبيوتر is literally on the computer, which matches normal English usage pretty well.

In this sentence, it means that the action is done using the computer as the writing medium:

• تكتب على الكمبيوتر = write/type on the computer

This is a very natural expression in Egyptian Arabic.

Yes, الكمبيوتر has the definite article الـ, so literally it is the computer.

In everyday Arabic, especially with tools, devices, and common activities, the definite article is often used where English might say either the or nothing special:

• على الكمبيوتر can mean on the computer
• depending on context, it can also feel more general, like using a computer

So even if English might sometimes say on a computer, Arabic very naturally says على الكمبيوتر.

Yes, that is also natural.

Compare:

• أختي عارفة تكتب على الكمبيوتر
• أختي بتعرف تكتب على الكمبيوتر

Both can mean roughly My sister knows how to write/type on the computer.

The difference is mainly in style and nuance:

• عارفة uses the active participle and often feels a bit like a state: she knows
• بتعرف uses the regular present-tense verb and feels a bit more verbal: she knows / she is able to

In many everyday situations, the meanings overlap a lot.