A haladó úszó a rajtkő mellett vár.

Here haladó means advanced or higher-level.

It comes from the verb halad, meaning to progress or to move forward. In many learning contexts, haladó is used like advanced in English, as in haladó diák = advanced student.

So haladó úszó means advanced swimmer, not just a swimmer who is physically moving forward.

Because a is the Hungarian definite article, meaning the.

So:

• A haladó úszó = the advanced swimmer
• a rajtkő mellett = next to the starting block / literally beside the starting block

Hungarian uses the definite article very regularly. Also, the form is:

• a before a consonant
• az before a vowel

So you get a rajtkő, but az asztal.

Because egy means a/an, while a/az means the.

So:

• egy haladó úszó = an advanced swimmer
• a haladó úszó = the advanced swimmer

If the sentence is talking about a specific swimmer already known in the context, a is the natural choice.

Rajtkő is the word used for a starting block in swimming.

It is a compound word:

• rajt = start
• kő = stone

Even though kő literally means stone, the whole compound rajtkő means the swimming starting block, not an actual stone.

Because mellett is a postposition.

In English, we use prepositions: they come before the noun:

• next to the starting block

In Hungarian, many such words come after the noun phrase:

• a rajtkő mellett = next to the starting block

So mellett means beside / next to, and it follows the noun.

Because mellett is a postposition, and postpositions usually follow a noun phrase in its basic form.

So Hungarian says:

• a rajtkő mellett

not something like rajtkőn mellett.

The location meaning is already expressed by mellett, so no extra case ending is needed on rajtkő here.

Here vár means waits.

It comes from várni = to wait.

It is not várja, because várja would usually mean waits for it/him/her and would require a definite object. For example:

• A buszt várja. = He/She is waiting for the bus.

But in your sentence, vár is used without a direct object:

• A haladó úszó a rajtkő mellett vár.
• The advanced swimmer is waiting beside the starting block.

So vár is the correct form.

Hungarian usually does not need a subject pronoun if the subject is already clear.

In this sentence, the subject is explicitly given:

• A haladó úszó

So there is no need to add ő (he/she).

Also, Hungarian verbs already show person and number. Here vár is third person singular: he/she waits.

No. Hungarian word order is more flexible than English word order.

This sentence:

• A haladó úszó a rajtkő mellett vár.

is natural and emphasizes the sentence in a normal, flowing way: As for the advanced swimmer, he/she is waiting next to the starting block.

You could also say:

• A haladó úszó vár a rajtkő mellett.

That is also correct. The difference is mostly about emphasis and information structure, not basic meaning.

Hungarian often places important information just before the verb, so word order can shift depending on what the speaker wants to highlight.

Because Hungarian adjectives do not work like adjectives in many Indo-European languages.

A few important points:

• Hungarian has no grammatical gender, so there is no masculine/feminine agreement.
• Attributive adjectives usually stay unchanged before the noun.
• The noun carries the main number and case marking.

So:

• haladó úszó = advanced swimmer
• haladó úszók = advanced swimmers

Notice that haladó stays the same.

In this sentence, úszó means swimmer.

It comes from úszni = to swim. Hungarian often uses a verb-based form like this as a noun or adjective depending on context.

So:

• úszó can function as swimmer
• in other contexts, similar forms can behave more adjectivally

Here, because it follows haladó and refers to a person, haladó úszó is clearly understood as advanced swimmer.

The long vowel ő is a sound English does not have exactly.

A rough guide:

• ő is a long, rounded front vowel
• it sounds somewhat like the vowel in French peu, but held longer

So rajtkő is approximately:

• rajt-kő

with a clear long final vowel.

Also, ő and o/ó are different sounds in Hungarian, so it is worth learning them separately.