Részben értem a panaszt.

It is built from rész = part and -ben = in.

So literally részben means in part, and in normal English that is usually partly or partially. In this sentence, it works as an adverb.

Because Hungarian has two main verb conjugation patterns: indefinite and definite.

Here the object is a panaszt = the complaint, which is definite, so the verb uses the definite conjugation:

• értek = I understand something / I understand in general
• értem = I understand it / the specific thing

So Részben értem a panaszt uses értem because the speaker is talking about a specific complaint.

Hungarian has two forms of the definite article:

• a before a consonant
• az before a vowel

Since panaszt begins with p, a consonant, the correct form is a panaszt.

The ending -t marks the accusative case, which is the case used for a direct object.

The basic noun is panasz = complaint.
As the direct object of értem, it becomes panaszt.

So:

• panasz = complaint
• panaszt = complaint, as the thing being understood

Not every Hungarian noun needs a linking vowel before -t.

Some nouns simply add -t directly, and panasz is one of them:

• panasz → panaszt

Hungarian accusative forms are not always completely predictable from English habits, so this is something you gradually get used to as vocabulary.

The dictionary form is panasz.

In the sentence, panaszt is singular accusative. It refers to one complaint, not several.

If it were plural accusative, it would be panaszokat.

Putting részben first is very natural in Hungarian. It sets the frame right away: the speaker is saying that their understanding is only partial.

Hungarian word order is more flexible than English word order, and it often reflects emphasis or information structure rather than a fixed pattern. Here, sentence-initial részben slightly highlights the idea of only partly.

Yes, but the emphasis would change.

For example:

• Részben értem a panaszt.
  Natural, with emphasis on partly

• A panaszt részben értem.
  Also possible, but it puts more attention on the complaint

Hungarian word order is often about what you want to foreground. So the sentence you were given is a very natural way to say it.

Yes, there is a nuance.

• értem a panaszt = I understand the complaint
• megértem a panaszt = I understand the complaint / I can see why / I sympathize with it a bit more strongly

The prefix meg- often gives a sense of completed or fuller understanding. So megértem can sound a little stronger or more like I can understand that.

With részben, both are possible, but they are not exactly identical in tone.

A rough pronunciation is:

[reːsben ˈeːrtɛm ɒ ˈpɒnɒst]

A few useful points:

• sz is pronounced like English s
• é is a long e sound
• a in Hungarian is not the same as English a in cat; it is closer to the vowel in British-style hot for many learners
• panaszt ends with a consonant cluster that sounds roughly like pah-nahst

So részben is roughly RAYSS-ben, and értem is roughly AYR-tem, though those English approximations are only approximate.

You can tell from the grammar of the sentence.

Here értem is followed by a panaszt, which is a direct object. That fits the verb érteni = to understand.

The other értem is not the same word grammatically. It is a different form used in expressions meaning for me or because of me. In this sentence, the structure clearly shows that értem is the verb.