حسنا، أفهم.

A careful MSA reading is approximately:

• حسنًا → ḥasanan
• أفهم → afhamu

A few notes:

• ح is not exactly the English h. It is a stronger, deeper breathy sound.
• أ at the start of أفهم is a glottal stop, like the catch in the middle of uh-oh.
• At the end of a sentence, Arabic often drops the final short vowel in pronunciation, so أفهمُ may sound more like afham in pause.

حسنًا works like okay, all right, or fine at the start of the sentence.

Literally, it comes from a word meaning good or well, but here it functions as a discourse word: it helps manage the conversation rather than describing something.

So the sentence feels like:

• Okay, I understand.

The ending -an is the accusative ending, called tanwīn fatḥ.

In expressions like حسنًا, Arabic often uses the accusative to make an adverbial expression, somewhat like well or fine in English.

So:

• حسنًا is the standard MSA form
• the -an ending is normal here

In everyday printed Arabic, the diacritics are usually left out, so you may just see حسنا.

That final ا is a normal spelling feature that often appears with the -an ending in Arabic.

So although the word is pronounced with an -an ending in connected speech, it is commonly written with that final ا. When diacritics are included, you see حسنًا; when they are not, you usually see حسنا.

This is a spelling pattern, not a separate word part with its own meaning.

أفهم is a first-person singular imperfect verb, meaning I understand.

It comes from the verb:

• فَهِمَ = to understand

So:

• أفهم = I understand
• in fully marked MSA, it is أفهمُ

The imperfect tense in Arabic often corresponds to the English present tense.

Because Arabic verbs usually include the subject inside the verb itself.

In أفهم, the prefix أ- already tells you the subject is I.

So:

• أفهم = I understand

You can add أنا if you want emphasis or contrast:

• أنا أفهم = I understand / I do understand

But in a normal sentence, أنا is not necessary.

The أ at the beginning is not part of the root. It is the prefix used for I in the imperfect tense.

The root is still:

• ف-ه-م

Compare:

• أفهم = I understand
• تفهم = you understand or she understands
• يفهم = he understands
• نفهم = we understand

So the beginning letter changes with the subject.

If you are reading fully inflected MSA carefully, yes: أفهمُ ends with -u.

But two important things are true:

• most normal Arabic text leaves off short-vowel marks, so you usually just see أفهم
• when stopping at the end of a sentence, Arabic commonly drops the final short vowel in pronunciation

So in practice, learners will often hear something like afham at the end of the sentence, even though the full grammatical form is أفهمُ.

Arabic, like English, can leave the object unstated when it is obvious from context.

So أفهم can mean:

• I understand
• I understand it
• I understand what you mean

The missing object is simply understood from the situation.

They are close, but not identical:

• أفهم = I understand
• فهمت = I understood / I got it

So أفهم sounds more like a present-state statement, while فهمت often sounds more immediate or completed.

In conversation, both may be translated naturally into English depending on context, but the grammar is different.

It is the Arabic comma.

Arabic punctuation is similar to English punctuation in function, but some marks look different. So:

• ، = comma
• ؟ = question mark

In حسنًا، أفهم., the comma separates the opening discourse word حسنًا from the main statement أفهم.

Yes. حسنًا، أفهم. is natural and correct in MSA.

A small nuance:

• أفهم is completely standard for I understand
• حسنًا is also standard, but it can sound a little more formal or bookish than what many people would say in everyday dialect conversation

So this sentence is very suitable for formal Arabic, writing, subtitles, dubbing, and classroom MSA.