Kraj filma je bio dobar.

Because kraj normally takes the genitive case in Serbian.

So:

• film = movie / film (dictionary form, nominative)
• filma = of the movie / movie's (genitive singular)

In kraj filma, the literal structure is:

• kraj = end
• filma = of the movie

So the whole phrase means the end of the movie.

This is a very common pattern:

• kraj dana = the end of the day
• kraj godine = the end of the year
• kraj puta = the end of the road

Kraj is in the nominative singular.

In this sentence, kraj filma is the subject:

• Kraj filma = the end of the movie
• je bio dobar = was good

So kraj is nominative because it is the main noun of the subject, while filma is genitive because it depends on kraj.

Serbian does not use articles like English a and the.

So Kraj filma je bio dobar can mean:

• The end of the movie was good
• or, depending on context, An ending of a movie was good

In real usage, context usually makes it clear that it means the end of the movie.

This is normal in Serbian. You usually do not translate the word-for-word.

Serbian past tense is usually formed with:

• the present tense of biti (to be) as an auxiliary
• plus the past participle

Here:

• je = auxiliary (is/has, but here used to form the past)
• bio = past participle of biti

Together, je bio means was.

So:

• je bio = he/it was
• je bila = she/it was
• je bilo = it was (neuter)

Even though English uses one word, Serbian often uses two.

Because bio must agree with kraj, and kraj is masculine singular.

In Serbian, the past participle agrees in gender and number with the subject.

So:

• kraj is masculine singular
• therefore: bio dobar

Compare:

• Priča je bila dobra. = The story was good.
  (priča is feminine)
• Pismo je bilo dobro. = The letter was good.
  (pismo is neuter)

Because dobar is an adjective describing kraj, and adjectives must agree with the noun they describe.

Since kraj is masculine singular, the adjective is also masculine singular:

• dobar = masculine singular
• dobra = feminine singular
• dobro = neuter singular

So:

• kraj → dobar
• priča → dobra
• mesto → dobro

English learners often confuse dobar and dobro because dobro can also be an adverb meaning well.

For example:

• Film je dobar. = The movie is good.
• On peva dobro. = He sings well.

Word by word:

• kraj = end
• filma = of the movie / of the film
• je = is / auxiliary used in the past tense
• bio = been / was (past participle of biti)
• dobar = good

A more literal breakdown is:

• Kraj filma = end of the movie
• je bio = was
• dobar = good

Yes. Film is the standard and very common word for film/movie.

So in everyday Serbian:

• film = movie / film

If the meaning has already been shown to you, you can safely think of film as the usual word for movie in most contexts.

Yes, Serbian word order is more flexible than English word order.

The neutral, standard order is:

• Kraj filma je bio dobar.

But you may also hear variations such as:

• Dobar je bio kraj filma.
• Kraj filma bio je dobar.

These can sound slightly different in emphasis or style, but the basic meaning stays the same.

For learners, the safest pattern is the original one:

• subject + je + past participle + adjective

Yes, but the meaning is slightly different.

• Kraj filma je bio dobar. = The end of the movie was good.
  This refers to a completed past experience.
• Kraj filma je dobar. = The end of the movie is good.
  This sounds more like a general statement or opinion about the movie.

So both are correct, but je bio places the statement clearly in the past.

Yes, if the context already makes it clear what end you mean.

• Kraj je bio dobar. = The ending was good.

This is natural if everyone already knows you are talking about a movie, book, story, etc.

But if you want to be specific, kraj filma is clearer.

It is used for both.

Kraj can mean:

• the end of something in space
• the end of something in time
• the ending of a story, movie, book, etc.

So in Kraj filma je bio dobar, it clearly means the ending of the movie.

A simple pronunciation guide is:

Kray FIL-ma yeh BEE-oh DOH-bar

A few notes:

• j in Serbian sounds like English y
• je sounds roughly like ye
• bio is usually said as two syllables: bi-o
• stress is not usually marked in normal writing, so learners often just imitate native audio at first

If you read it slowly:

Kraj / filma / je / bio / dobar

that will already sound quite understandable.

The structure is:

[noun phrase] + [auxiliary] + [past participle] + [adjective]

So here:

• Kraj filma = subject noun phrase
• je bio = past form of to be
• dobar = predicate adjective

This is a very common Serbian pattern for saying that something was a certain way:

• Film je bio zanimljiv. = The movie was interesting.
• Dan je bio dug. = The day was long.
• Početak je bio loš. = The beginning was bad.

So this sentence is a very useful model to learn from.