Publiczność długo bije brawo po koncercie.

Yes, it refers to many people, but publiczność is a collective noun in Polish, like the audience in English. Grammatically, it is singular, so the verb must also be singular.

That is why you get:

• Publiczność bije brawo = The audience applauds

not:

• Publiczność biją brawo ✗

Also, publiczność is grammatically feminine singular, although in the present tense that does not change the form here.

Yes. Bić brawo is a very common Polish expression meaning to applaud / to clap.

Literally, bić usually means to beat / to hit, but in this expression it does not mean that literally. You should learn bić brawo as a set phrase.

So:

• bić brawo = to applaud
• Publiczność bije brawo = The audience applauds

A close synonym is klaskać, which also means to clap.

In the expression bić brawo, the word brawo is normally treated as a fixed, indeclinable form. In other words, it stays brawo in this phrase.

So you say:

• bić brawo
• bił brawo
• biją brawo

This is just how the idiom works.

You may also come across brawa in other expressions, for example:

• dostać brawa = to receive applause
• słychać brawa = applause can be heard

But in bić brawo, the usual form is brawo.

Because długo is an adverb, and it describes how long the action lasts.

Here it modifies the verb:

• bije brawo długo = applauds for a long time

Polish uses:

• długi / długa / długie for adjectives, describing nouns
• długo for adverbs, describing verbs

Compare:

• długi koncert = a long concert
• Publiczność długo bije brawo = The audience applauds for a long time

Po here means after, and when po is used in this temporal sense, it takes the locative case.

So:

• koncert = concert
• po koncercie = after the concert

This is why the noun changes from koncert to koncercie.

More examples:

• po obiedzie = after dinner
• po filmie = after the film
• po lekcji = after class

It can definitely move. Polish word order is more flexible than English word order.

All of these are possible:

• Publiczność długo bije brawo po koncercie.
• Po koncercie publiczność długo bije brawo.
• Publiczność po koncercie długo bije brawo.

The basic meaning stays the same, but the emphasis can shift slightly.

For example:

• Po koncercie at the beginning puts more focus on when
• długo placed earlier can emphasize the length of the applause

Bije is the 3rd person singular present tense of bić.

So literally it means:

• is applauding
• applauds

Like many present-tense forms in Polish, it can be used in different ways depending on context:

• for something happening now
• for a general/habitual statement
• sometimes in vivid narration

In a simple sentence like this, it most naturally means something like:

• The audience is applauding for a long time after the concert or
• The audience applauds for a long time after the concert

Yes, absolutely. That is also correct and natural.

• bić brawo = to applaud
• klaskać = to clap

So:

• Publiczność długo bije brawo po koncercie
• Publiczność długo klaszcze po koncercie

Both are fine. The first one may feel a bit more idiomatic as applaud, while klaskać focuses more directly on the act of clapping.

Because Polish has no articles like a, an, or the.

So:

• publiczność can mean the audience or an audience
• koncert can mean the concert or a concert

You understand which one is meant from the context.

Here, English naturally uses the:

• The audience applauds for a long time after the concert

But Polish does not need a separate word for that.

A rough guide:

• publiczność ≈ poob-LEECH-noshch
• koncercie ≈ kon-TSER-chye

A few useful pronunciation points:

• cz sounds roughly like ch in chop
• ć / ci sounds like a softer ch
• ś / ź / ń / ć are soft consonants
• ń sounds a bit like ny in canyon
• ść at the end of publiczność is a consonant cluster that may take practice

If you want to sound natural, it helps to listen to native audio, especially for endings like -cie and -ność.

In normal everyday Polish, publiczność is generally treated as a singular collective noun. You normally use it the way English uses audience.

So you say:

• Ta publiczność jest wspaniała. = This audience is wonderful.
• Publiczność bije brawo. = The audience applauds.

A plural form is not commonly used in ordinary speech for the general meaning of audiences. Usually Polish expresses that idea in some other way, depending on context.

So for a learner, the safest rule is:

• treat publiczność as singular

You would change the verb from present bije to past biła, because publiczność is grammatically feminine singular.

So:

• Publiczność długo biła brawo po koncercie. = The audience applauded for a long time after the concert.

This is a good example of how the grammatical gender of publiczność matters in the past tense:

• biła = feminine singular past

If the subject were a masculine personal plural noun, the verb would look different.

The natural English meaning is applauds for a long time.

Polish often uses an adverb like długo without needing an extra word equivalent to English for in this kind of phrase.

So:

• długo czekać = to wait a long time
• długo spać = to sleep a long time
• długo bić brawo = to applaud for a long time

So even though the Polish sentence does not literally include for, that is how it is normally understood in English.