A közösség nagy.

No. In Hungarian, a is the definite article, so it means the, not a/an.

• a közösség = the community
• egy közösség = a community

A useful thing to know is that Hungarian has two forms of the definite article:

• a before most consonant sounds
• az before vowel sounds

So here, a közösség means the community.

Hungarian often leaves out the verb to be in the present tense, third person.

So English:

• The community is big.

becomes Hungarian:

• A közösség nagy.

There is no separate word for is here.

This happens when the subject is he/she/it or a noun like the community, and the predicate is a noun, adjective, or similar expression.

Compare:

• Én nagy vagyok. = I am big.
• Te nagy vagy. = You are big.
• A közösség nagy. = The community is big.

So the missing is is completely normal.

Here, nagy is not directly describing the noun inside a noun phrase. It is the predicate adjective: it tells us what the community is like.

So:

• A nagy közösség = the big community
  Here nagy comes before the noun because it is directly modifying it.

But:

• A közösség nagy. = The community is big.
  Here nagy is the main statement about the subject, so it comes later.

That is the same difference as:

• the big house
• the house is big

A simple learner-friendly pronunciation guide is:

• A ≈ short aw
• közösség ≈ kuh-ZOESH-shayg (very approximate)
• nagy ≈ nawdy or nody with a soft dy sound

A few important sound notes:

• ö is a rounded front vowel, somewhat like German ö or French eu
• é is a long vowel, like ay in say, but pure and steady
• gy is a soft consonant, somewhat like the d in British duke or a softened dy

Hungarian pronunciation is usually quite regular, so once you learn the sound values, spelling is very helpful.

In Hungarian, accents are part of the spelling, not optional marks.

In közösség:

• ö is a different vowel from o
• é is a different vowel from e, and it is long

So these marks change pronunciation and can also distinguish different words. You should treat accented letters as full letters in their own right.

Hungarian vowels commonly appear in short and long pairs, for example:

• e / é
• o / ó
• ö / ő
• u / ú
• ü / ű

Közösség is the subject of the sentence, and it is in the nominative form, which is the basic dictionary form.

So:

• a közösség = the community → subject
• nagy = big → predicate adjective

There is no special ending here because the noun is simply the subject.

Yes. Hungarian word order is flexible, and changing it often changes focus or emphasis, not the core meaning.

For example:

• A közösség nagy. = neutral statement: The community is big.
• Nagy a közösség. = puts more emphasis on big or on the fact of largeness

Both are grammatical, but they are not used in exactly the same discourse situation. The version you were given, A közösség nagy., is the more straightforward neutral form.

Often yes, but like English big, it can be used in a few related ways depending on context.

It can mean things like:

• big
• large
• sometimes great or important, depending on the sentence

In A közösség nagy., the most natural meaning is simply that the community is large or big.

You add nem before the predicate:

• A közösség nem nagy.

That is the normal way to negate this kind of sentence.

Because there is no overt is in the affirmative sentence, you just negate the adjective phrase directly with nem.

You can add nagyon before the adjective:

• A közösség nagyon nagy.

Here:

• nagyon = very
• nagy = big

So the structure is very straightforward.

These look similar, but they mean different things grammatically.

• A nagy közösség = the big community
  This is a noun phrase, not a complete sentence by itself.

• A közösség nagy. = The community is big.
  This is a complete sentence.

So the position of nagy matters:

• before the noun = attributive adjective
• after the noun, as the statement = predicate adjective

In the plural, both the noun and the adjective usually show plural marking:

• A közösségek nagyok. = The communities are big.

Here:

• közösségek = communities
• nagyok = big (plural form)

This is a useful contrast with the singular:

• A közösség nagy. = The community is big.
• A közösségek nagyok. = The communities are big.

Yes. A közösség nagy. is a normal, grammatical, complete Hungarian sentence.

That said, by itself it may sound a little context-free, just as The community is big can sound a bit isolated in English. In real conversation, it would often appear with more context, but grammatically it is perfectly natural.