A lakodalom helyszíne szép.

A is the definite article, like the in English.

In Hungarian possessive phrases, the article usually goes in front of the whole possessive group, so:

a lakodalom helyszíne

means something like:

the wedding's venue / the venue of the wedding

So even though helyszíne is the main noun, the article appears before lakodalom because the whole phrase starts there.

Because helyszíne is the possessed form.

• helyszín = venue / location
• helyszíne = its venue or the venue of it

Here, the possessor is lakodalom, so lakodalom helyszíne literally works like:

wedding venue-its

That is how Hungarian often expresses the venue of the wedding.

The ending -e is the 3rd person singular possessive suffix used here.

Hungarian possessive structure is often:

possessor + possessed noun with possessive suffix

So:

• lakodalom = the possessor
• helyszíne = the possessed noun

Literally, it is closer to:

wedding its-venue

but in natural English we say:

the wedding's venue or the venue of the wedding

Hungarian does not need a separate word like of here.

There is also a more explicit version:

A lakodalomnak a helyszíne szép.

Here -nak marks the possessor more clearly, but the shorter version in your sentence is very normal.

In this kind of sentence, Hungarian usually leaves it out.

So:

A lakodalom helyszíne szép.

has no written word for is, but it still means is beautiful.

This happens in the present tense with third person subjects when the predicate is a noun or adjective.

Compare:

• A helyszín szép. = The venue is beautiful.
• A helyszín nagy. = The venue is big.

But in other situations, Hungarian does use the copula:

• A helyszín szép volt. = The venue was beautiful.
• Szép vagyok. = I am beautiful.
• A helyszín a városban van. = The venue is in the city.

That is a very natural neutral word order in Hungarian.

The sentence is structured like:

topic / subject + predicate

So:

• A lakodalom helyszíne = what we are talking about
• szép = what is being said about it

Hungarian word order is flexible, though. You can also say:

Szép a lakodalom helyszíne.

This is still grammatical, but it gives more emphasis or focus to szép. It can sound a bit more like:

The wedding venue is beautiful
with extra attention on beautiful.

Not always.

A useful rough distinction is:

• esküvő = the wedding ceremony
• lakodalom = the wedding celebration, feast, or party

In everyday speech, people may sometimes use them more loosely, but lakodalom often suggests the festive event rather than just the formal ceremony.

So this sentence may sound more like it is talking about the venue for the wedding celebration.

Here, no. Since the subject is singular, szép stays as szép.

In Hungarian, predicate adjectives can show plural when the subject is plural:

• A lakodalom helyszíne szép. = singular
• A lakodalmak helyszínei szépek. = plural

So:

• szép = beautiful, singular
• szépek = beautiful, plural predicate form

That said, adjectives placed directly before a noun do not behave the same way:

• szép helyszín
• szép helyszínek

So learners often notice that Hungarian adjective agreement works differently from English and from many European languages.

A learner-friendly breakdown is:

• A = the
• lakodalom = wedding celebration
• helyszíne = its venue / venue of it
• szép = beautiful

So the grammar is not word-for-word English, but the internal logic is:

The wedding celebration's venue beautiful.

Then natural English turns that into the usual sentence you were shown.