לא לגמרי הבנתי מה היא אמרה, אבל אחר כך קראתי את ההודעה שוב.

Because the verb form already tells you the subject. In the past tense, the ending -תי means I.

• הבנתי = I understood
• קראתי = I read

So Hebrew often leaves out אני when it is not needed. If you added it, it would usually sound more emphatic: אני הבנתי = I understood / I was the one who understood.

לא לגמרי means not completely, not entirely, or not quite.

So לא לגמרי הבנתי is a very natural way to say I didn’t completely understand or I didn’t quite understand.

It is slightly softer than a plain לא הבנתי (I didn’t understand), because it suggests partial understanding rather than total confusion.

Both are possible, and both can mean I didn’t completely understand.

The version in your sentence, לא לגמרי הבנתי, is very natural and puts early emphasis on not completely.
The alternative לא הבנתי לגמרי is also common.

So this is mostly a matter of word order and emphasis, not a big grammar difference.

This is an embedded question, meaning what she said.

Literally:

• מה = what
• היא = she
• אמרה = said

So לא לגמרי הבנתי מה היא אמרה is literally something like I didn’t completely understand what she said.

Hebrew often uses the question word directly in this kind of clause, just like English does.

That is a very common learner question.

Yes, אמרה by itself already shows she said, because it is third-person feminine singular in the past tense. But Hebrew often still includes the subject pronoun, especially in the third person, because it sounds natural and keeps the sentence clear.

So:

• מה היא אמרה = very natural
• מה אמרה = grammatically possible in some contexts, but less natural here for most speakers

By contrast, with I forms like הבנתי and קראתי, the pronoun is more often omitted.

Because the speaker is talking about a female person. In the Hebrew past tense, the verb agrees with the subject’s gender.

• אמרה = she said
• אמר = he said

So if the person were male, the sentence would be: לא לגמרי הבנתי מה הוא אמר...

אבל means but, and אחר כך means afterwards, later, or after that.

So:

• אבל = but
• אחר כך = afterward / later

Together, אבל אחר כך means but afterward or but later.

Also note that אחר כך is a fixed two-word expression.

את is the direct object marker. It has no English translation here, but it is used before a definite direct object.

So in: קראתי את ההודעה the word את marks ההודעה as the specific thing being read.

This is one of the most important grammar points in Hebrew:

• קראתי הודעה = I read a message / I was reading a message (indefinite)
• קראתי את ההודעה = I read the message (definite, specific)

The base word is הודעה = message, notice, notification, depending on context.

When you add the definite article ה- (the) to a noun that already begins with ה, both letters appear in writing:

• הודעה = message
• ההודעה = the message

So the double ה is just the article plus the first letter of the noun.

It is pronounced roughly ha-hoda'a.

שוב means again.

So: קראתי את ההודעה שוב = I read the message again

Putting שוב at the end is very natural in Hebrew. It comes after the object here, just as adverbs often do.

Other word orders are sometimes possible, but קראתי את ההודעה שוב is a standard, neutral way to say it.

Sometimes yes, but the meaning and feel are slightly different.

• מה היא אמרה = what she said as an indirect question
• מה שהיא אמרה = more like what it was that she said / the thing that she said

In your sentence, לא לגמרי הבנתי מה היא אמרה is the most natural everyday choice.

לא לגמרי הבנתי את מה שהיא אמרה is possible, but it sounds a bit heavier and less simple.

All the main verbs here are in the past tense:

• הבנתי = I understood
• אמרה = she said
• קראתי = I read

A useful pattern to notice:

• -תי often marks I in the past tense: הבנתי, קראתי
• -ה often marks she in the past tense: אמרה

So this sentence is describing a sequence of past actions: first the speaker did not fully understand, and later the speaker reread the message.

A simple transliteration is:

Lo legamrei hevanti ma hi amra, aval akhar kakh karati et hahoda'a shuv.

A few pronunciation notes:

• ח and כ in אחר כך are throaty sounds, like the ch in Scottish loch or German Bach
• הודעה is pronounced roughly ho-da-AH, with the stress at the end
• שוב sounds like shoov

So the rhythm is roughly:

lo le-gam-REI he-VAN-ti ma hi am-RA, a-VAL a-KHAR kakh ka-RA-ti et ha-ho-da-A shuv