Az önkéntesek összegyűjtik az üveghulladékot.

Az is the Hungarian definite article, so it means the.

It appears twice because both the subject and the object are definite:

• az önkéntesek = the volunteers
• az üveghulladékot = the glass waste

Hungarian has two forms of the definite article:

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

Since önkéntesek begins with ö and üveghulladékot begins with ü, the correct form is az in both places.

The singular form is önkéntes, meaning volunteer.

The ending -ek makes it plural here:

• önkéntes = volunteer
• önkéntesek = volunteers

Hungarian has several plural endings, and -k is the core plural marker. The vowel before it can vary depending on vowel harmony and pronunciation, so here you get -ek.

It comes from:

• gyűjt = collect, gather
• össze- = together, up

So összegyűjtik means something like they collect it up, they gather it together, or they collect it completely.

The prefix össze- often adds the idea of bringing things together into one place or completing the collecting action. So this is a bit more specific than just gyűjtik.

This is because Hungarian verbs have two main conjugation patterns:

• indefinite conjugation
• definite conjugation

Here the object is definite: az üveghulladékot. Because of that, Hungarian uses the definite verb form:

• gyűjtik = they collect it / they collect the ...
• gyűjtenek = they collect something non-specific

So:

• Önkéntesek üveghulladékot gyűjtenek = Volunteers collect glass waste / some glass waste
• Az önkéntesek az üveghulladékot gyűjtik = The volunteers collect the glass waste

Also, -ik here does not mean this is an -ik verb. It is just the 3rd person plural ending in the definite conjugation.

Because it is the direct object of the verb, and Hungarian usually marks direct objects with the accusative ending -t.

So:

• üveghulladék = glass waste
• üveghulladékot = glass waste, as the object

The full ending looks like -ot, not just -t, because Hungarian often inserts a linking vowel before the case ending to make pronunciation easier.

Yes. Hungarian forms compound nouns very freely.

This word is made from:

• üveg = glass
• hulladék = waste

So üveghulladék literally means glass waste.

English often writes similar expressions as two words, but Hungarian commonly combines them into one compound word.

Because üveghulladék is being used as a mass or collective noun, much like waste in English.

So Hungarian is not talking about separate individual objects one by one. It is treating the material as a category or substance:

• üveghulladék = glass waste, waste glass

This is very natural in Hungarian. Even if the waste consists of many pieces or bottles, the noun can stay singular.

No. Hungarian word order is flexible, and changing it can change the emphasis.

The given sentence is a normal neutral order:

• Az önkéntesek összegyűjtik az üveghulladékot.

This presents the volunteers as the topic, then says what they do.

Other word orders are possible for emphasis. For example:

• Az üveghulladékot az önkéntesek gyűjtik össze.
  This puts more emphasis on the glass waste and on the volunteers as the ones who collect it.

A useful thing to notice is that the verbal prefix össze- may separate from the verb in some sentence patterns, especially when something is strongly focused.

In a neutral statement, the prefix usually stays attached:

• összegyűjtik

But in sentences with focus, negation, or certain other structures, the prefix can move:

• Az üveghulladékot gyűjtik össze.
• Nem gyűjtik össze az üveghulladékot.

This is very common in Hungarian. So the dictionary-style form may look like one word, but in real sentences the prefix is sometimes separated.

A few sounds here are unusual for native English speakers:

• ö as in önkéntesek
  A front rounded vowel. Roughly like German ö or French eu in some words.

• ü as in üveghulladékot and gyűjtik
  Another front rounded vowel. Roughly like German ü or French u.

• gy as in gyűjtik
  This is a soft consonant sound, somewhat like the d sound in British English duke or during, but it is best learned as its own Hungarian sound.

A rough pronunciation guide for the whole sentence would be:

• Az önkéntesek összegyűjtik az üveghulladékot
• approximately: awz urn-kayn-teh-shek uhs-seh-dyoo-ee-tik awz oo-vehg-hool-lah-day-kot

That is only approximate, but it can help you get started.