Filmové plátno je velké.

Because they both agree with plátno, which is a neuter singular noun.

In Czech, adjectives change their endings to match the noun’s:

• gender
• number
• case

Here:

• plátno = neuter singular
• filmové = neuter singular form of filmový
• velké = neuter singular form of velký

So the matching is:

• masculine: filmový plakát je velký
• feminine: filmová kamera je velká
• neuter: filmové plátno je velké

Plátno is in the nominative singular, because it is the subject of the sentence.

The adjective filmové is also nominative singular neuter, because it directly describes plátno.

The adjective velké is also in the nominative singular neuter form, because after je it functions as a predicate adjective and still agrees with the subject.

So the structure is:

• Filmové plátno = subject
• je = is
• velké = predicate adjective, agreeing with the subject

A very common clue is the ending -o. Many Czech nouns ending in -o are neuter.

So:

• plátno = neuter
• nominative singular form = plátno

This is not an absolute rule for every word in Czech, but it is a very useful pattern.

Because plátno is neuter, the adjectives around it also take neuter endings:

• filmové
• velké

Not always. Plátno has a broader meaning than just screen.

It can mean:

• canvas
• cloth
• screen, especially a projection screen

So filmové plátno literally means something like film/cinema screen or movie screen.

The adjective filmové narrows the meaning and makes it clear that this is a screen used for films, not just any piece of canvas.

Czech does not have articles like English the and a/an.

So Filmové plátno je velké could mean:

• The movie screen is big
• A movie screen is big

Which one sounds best depends on the context.

Czech usually expresses definiteness through:

• context
• word order
• stress
• surrounding sentences

So the lack of the is completely normal.

Je is the 3rd person singular form of být = to be.

So:

• je = is

In this sentence, it is necessary in normal standard Czech:

• Filmové plátno je velké. = The movie screen is big.

Unlike in some languages, standard Czech normally does not omit is in ordinary sentences like this.

Yes, Czech word order is more flexible than English, but the neutral, most straightforward order here is:

• Filmové plátno je velké.

You could also hear:

• Velké je filmové plátno.
• Filmové plátno velké je. — possible, but marked or poetic
• Je velké filmové plátno. — possible in a different context

However, changing the order usually changes the focus or emphasis, not the basic meaning.

For a learner, the best default is:

• subject + je + adjective
• Filmové plátno je velké.

A simple approximate pronunciation is:

• Filmové ≈ FIL-mo-vay
• plátno ≈ PLAAT-no
• je ≈ ye
• velké ≈ VEL-kay

A few useful pronunciation notes:

• á is a long a
• é is a long e sound, roughly like ay in careful approximation
• j is pronounced like English y in yes
• stress in Czech normally falls on the first syllable of each word:
  • FILmové
  • PLÁTno
  • JE
  • VELké

Yes. Veliké is also possible and means essentially big/large too.

So you could say:

• Filmové plátno je velké.
• Filmové plátno je veliké.

But velké is the more common everyday word.

Both adjectives still have to agree with plátno, so they appear in the neuter singular form:

• velké
• veliké

It is an adjective.

The base noun is:

• film = film/movie

From that, Czech forms the adjective:

• filmový = film, movie, cinematic

Then it changes to match plátno:

• masculine: filmový
• feminine: filmová
• neuter: filmové

So in this sentence:

• filmové plátno = movie screen / cinema screen

It is not a separate noun form here; it is just a normal agreeing adjective.