Hiszek az úszómesternek.

It is built into the verb hiszek.

In Hungarian, the verb usually shows the subject, so a separate pronoun is often omitted:

• hiszek = I believe
• hiszel = you believe
• hisz = he/she believes

You could say Én hiszek az úszómesternek, but én would add emphasis, like I believe the lifeguard.

Hiszek is the 1st person singular, present tense form of hinni (to believe).

So:

• hinni = to believe
• hiszek = I believe

This verb changes its stem in the present tense, so learners usually memorize it as:

• hiszek
• hiszel
• hisz

Because Hungarian uses the indefinite conjugation here.

A very important point: Hungarian uses the definite conjugation only when the verb has a definite direct object.

But in Hiszek az úszómesternek, az úszómesternek is not a direct object. It is in the dative case (-nek), because hisz takes a dative person:

• hisz valakinek = believe someone

So the verb stays hiszek, not hiszem.

Because the verb pattern is:

• hisz valakinek = believe someone
• literally, the person is marked with the dative ending -nak/-nek

So:

• úszómester = lifeguard
• úszómesternek = to the lifeguard / the lifeguard (as the person being believed)

In English, we say I believe the lifeguard, but Hungarian uses dative grammar here.

It means I believe the lifeguard — in other words, I believe what the lifeguard says.

That is different from believe in.

Compare:

• Hiszek az úszómesternek. = I believe the lifeguard.
• Hiszek az úszómesterben. = I believe in the lifeguard.

So:

• valakinek hisz = believe someone
• valakiben hisz = believe in someone

Hungarian has two forms of the definite article:

• a before a consonant sound
• az before a vowel sound

Since úszómesternek starts with ú, you use az:

• az úszómesternek

This is because of vowel harmony.

The dative ending has two forms:

• -nak after back-vowel words
• -nek after front-vowel words

Here the word is úszómester, and although it contains back vowels earlier, it is a compound, and compounds often harmonize with their last part. The last part is mester, which has a front vowel (e), so the correct form is:

• úszómesternek

Usually, yes.

If you mean a specific lifeguard, Hungarian normally uses the definite article:

• Hiszek az úszómesternek.

Leaving it out would sound unnatural in an ordinary sentence.

Yes. Hungarian word order is flexible, and changing it changes the emphasis.

• Hiszek az úszómesternek. = neutral, natural sentence
• Az úszómesternek hiszek. = puts more emphasis on the lifeguard, something like It’s the lifeguard I believe or As for the lifeguard, I believe him

So the original order is fine, but other orders are possible depending on focus.

It is a compound word:

• úszó = swimmer / swimming
• mester = master

Together, úszómester means lifeguard.

This is very common in Hungarian: longer words are often made by joining smaller words together.

Roughly:

• Hiszek ≈ HEE-sek
• az ≈ awz
• úszómesternek ≈ OO-soh-mesh-ter-nek

A few useful pronunciation points:

• sz sounds like English s
• s sounds like English sh
• ú and ó are long vowels
• stress is on the first syllable of each word

So úszómesternek starts with a stressed Ú.