Nož i viljuška su za meso, a kašika je za supu.

Because the subject changes:

• Nož i viljuška = knife and fork → two things, so Serbian uses su (are)
• Kašika = spoon → one thing, so Serbian uses je (is)

So:

• Nož i viljuška su... = The knife and fork are...
• Kašika je... = The spoon is...

These are present-tense forms of biti (to be).

A often links two clauses by contrasting them lightly or setting them side by side.

So here:

• Nož i viljuška su za meso, a kašika je za supu.

means something like:

• Knife and fork are for meat, while a spoon is for soup.

Comparison:

• i = and (simple addition)
• ali = but (stronger contrast)
• a = and / while / whereas (mild contrast)

In this sentence, a is the most natural choice because the speaker is comparing two different utensils and their uses.

Here za means for.

So:

• za meso = for meat
• za supu = for soup

In Serbian, za commonly takes the accusative case when it means for in this kind of purpose/use sentence.

Because Serbian nouns change by case, and different nouns have different endings.

After za, we use the accusative.

• meso is a neuter noun, and its accusative singular is the same as its nominative singular:
  • meso → meso
• supa is a feminine noun ending in -a, and in the accusative singular it changes to -u:
  • supa → supu

So:

• za meso
• za supu

This is a very common pattern in Serbian.

They are:

• nož = masculine
• viljuška = feminine
• kašika = feminine
• meso = neuter
• supa = feminine

This matters because gender affects adjective forms, pronouns, and case endings.

Because Serbian normally does not use articles.

English says:

• a knife
• the knife

Serbian usually just says:

• nož

The exact meaning depends on context.

So Nož i viljuška su za meso can mean:

• A knife and fork are for meat
• The knife and fork are for meat
• Knife and fork are for meat

depending on the situation.

Serbian often uses the singular to talk about something in a general, category-like way.

So:

• Nož i viljuška su za meso
  does not necessarily mean one specific knife and one specific fork. It can mean the utensils generally.

English can do something similar:

• A spoon is for soup.
• Spoons are for soup.

Both are possible. Serbian often prefers the singular in this kind of basic explanatory sentence.

A rough pronunciation guide:

• Nož ≈ nozh
  
  • ž sounds like the s in measure
• viljuška ≈ VEEL-yoosh-ka
  • š sounds like sh
  • j sounds like English y
• kašika ≈ KAH-shee-ka
• supu ≈ SOO-poo
• meso ≈ MEH-so

A useful letter guide here:

• š = sh
• ž = sound like s in measure
• j = y

They are standard and very common words, but regional variation exists.

For example:

• viljuška = fork is standard
• kašika = spoon is very common, especially in Serbian usage
• In some regions or related standards, you may also see žlica for spoon
• For soup, some speakers may say supa, while others may say juha

But in standard Serbian, viljuška, kašika, and supa are completely normal.

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

The original sentence is natural and neutral:

• Nož i viljuška su za meso, a kašika je za supu.

But other versions are possible for emphasis, for example:

• Za meso su nož i viljuška, a za supu kašika.

This sounds more marked and puts focus on what each utensil is for.

So yes, word order can change, but the original sentence is the best basic version for a learner.

It mainly describes normal use or purpose:

• A knife and fork are for meat, and a spoon is for soup.

It sounds like a general statement about what each utensil is used for. It does not sound especially strict or legalistic. It is just a simple explanatory sentence.

Yes, grammatically you could. The structure is fine.

For example:

• Nož i viljuška su za supu.
• Kašika je za meso.

These are grammatically correct, but they sound odd in meaning because they do not match normal usage. So the grammar is fine; the issue is just real-world logic.