Ponovna upotreba i reciklaža su važne.

Su is the present-tense form of biti (to be) for they are.

So:

• je = is
• su = are

Because the subject is made of two things — ponovna upotreba and reciklaža — Serbian uses the plural verb: su.

So structurally, this is:

• Ponovna upotreba i reciklaža = the subject
• su = are
• važne = important

Because važne is the plural feminine form of važan (important).

Both nouns in the subject are feminine singular nouns:

• upotreba = feminine
• reciklaža = feminine

When two feminine nouns are joined by i (and), the predicate goes into the plural, and the adjective agrees with that plural subject:

• singular feminine: važna
• plural feminine: važne

So:

• upotreba je važna = reuse is important
• reciklaža je važna = recycling is important
• upotreba i reciklaža su važne = reuse and recycling are important

Literally, it means something like repeated use or use again.

It is made of:

• ponovna = repeated / again / renewed
• upotreba = use

Together, ponovna upotreba is the standard way to say reuse.

A native English speaker may expect a single-word equivalent of reuse, but Serbian often uses a phrase like this instead.

They are in the nominative case, because they are the subject of the sentence.

The sentence is basically:

• Reuse and recycling = subject
• are important = predicate

In Serbian, subjects normally appear in the nominative.

I means and.

It links the two nouns:

• ponovna upotreba
• reciklaža

Just like in English, joining two singular nouns with and creates a plural subject, which is why the verb is su (are), not je (is).

A very common clue in Serbian is the ending -a.

Most nouns ending in -a are feminine, and both of these follow that pattern:

• upotreba
• reciklaža

Because they are feminine, the adjective forms connected with them are feminine too:

• singular: važna
• plural: važne

This is one of the most useful patterns for learners, although there are some exceptions elsewhere in the language.

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

The neutral version is:

• Ponovna upotreba i reciklaža su važne.

But you could also say:

• Važne su ponovna upotreba i reciklaža.

That version puts more emphasis on važne (important).

Even though word order can change, the standard sentence you were given is a very natural and straightforward one.

Because Serbian does not have articles like a / an / the.

So Serbian simply says:

• ponovna upotreba
• reciklaža

and context tells you whether English would use the, no article, or sometimes even a more general phrasing.

This is very normal in Serbian and other Slavic languages.

The letter ž is pronounced like the s in measure or the g in genre.

So:

• reciklaža sounds roughly like ret-see-KLA-zha
• važne sounds roughly like VAZH-neh

A few helpful pronunciation notes:

• ž = the sound in measure
• r is always clearly pronounced
• Serbian spelling is very phonetic, so words are usually pronounced much more like they are written than in English

Yes. The dictionary form is usually the masculine singular form:

• važan = important

From that, you get other forms:

• važan = masculine singular
• važna = feminine singular
• važno = neuter singular
• važni = masculine plural
• važne = feminine plural

So in your sentence, važne is used because the subject is plural and feminine.

Yes. A common alternative is bitne, which also means important in many contexts.

For example:

• Ponovna upotreba i reciklaža su važne.
• Ponovna upotreba i reciklaža su bitne.

Both are natural. Very roughly:

• važan often feels like important / significant
• bitan often feels like important / relevant / essential

In many everyday contexts, they overlap a lot.