أكتب بعض الأعراض في الاستمارة.

أكتب is the 1st-person singular imperfect form of كتب.

Here it means I write or I am writing. In Arabic, the imperfect can also sometimes express a near future meaning, depending on context, but the basic idea is present/imperfective.

Arabic often does not state the subject pronoun when the verb already shows it.

• أكتب already tells you the subject is I
• So أنا أكتب بعض الأعراض... is possible, but أنا is usually unnecessary unless you want emphasis or contrast

So the sentence is natural without أنا.

No. As written, أكتب with hamza above the alif means I write.

Compare:

• أكتب = I write
• اكتب = write! (command to one male)

In normal unvocalized writing, that hamza is an important clue.

After بعض (some), Arabic often uses a structure similar to some of the..., so بعض الأعراض is very common.

Grammatically:

• بعض = some / part
• الأعراض = the symptoms

Together, بعض الأعراض means some symptoms or literally some of the symptoms.

You can sometimes see بعض أعراض in other contexts, but بعض الأعراض is the more standard and expected phrasing for many learners.

Because بعض refers to more than one item here, the noun is plural.

• singular: عَرَض = a symptom
• plural: أَعْراض = symptoms

So:

• بعض الأعراض = some symptoms

This plural is a broken plural, which is very common in Arabic.

English and Arabic do not always use definiteness in the same way.

In Arabic, after words like:

• بعض = some
• كل = every/all
• معظم = most

the following noun is often definite. So بعض الأعراض is a very normal Arabic structure, even if English simply says some symptoms.

So do not translate the الـ too mechanically here.

Yes, in English we usually say on the form, but Arabic commonly uses في here.

• في literally means in
• في الاستمارة means something like in the form or on the form

This is just a difference in how the two languages use prepositions. It is best to learn في الاستمارة as a natural Arabic expression.

With full case endings, it would be:

أكتبُ بعضَ الأعراضِ في الاستمارةِ.

Breakdown:

• أكتبُ: verb in the indicative, ending in ـُ
• بعضَ: direct object, so accusative
• الأعراضِ: genitive because it follows بعض in an iḍāfa-like structure
• الاستمارةِ: genitive because it comes after في

In everyday writing, these endings are usually not written.

A careful pronunciation would be:

ʾaktubu baʿḍa l-aʿrāḍi fī l-istimārati

A few helpful notes:

• أكتب = ʾak-tu-bu
• بعض contains the letter ع, which has no exact English equivalent
• الأعراض is roughly al-aʿ-rāḍ
• الاستمارة is roughly al-is-ti-mā-ra

If you pause at the end of the sentence, the final short vowel is normally not pronounced.

Yes. This is a normal verbal sentence, beginning with a verb:

• أكتب = I write
• بعض الأعراض = some symptoms
• في الاستمارة = in/on the form

Verb-first order is very common in Arabic. You could also say:

أنا أكتب بعض الأعراض في الاستمارة

but that version sounds more emphatic because it explicitly mentions I.