Hi ha un paper amb la resposta al costat de l'ordinador.

Hi ha is the standard Catalan way to say there is or there are.

• ha comes from the verb haver
• hi is a little adverb-like element that is part of this expression

So:

• Hi ha un paper = There is a sheet of paper
• Hi ha dos papers = There are two sheets of paper

Even though English changes between there is and there are, Catalan normally keeps hi ha for both singular and plural.

Because paper is a masculine noun in Catalan.

So the indefinite article is:

• un for masculine singular
• una for feminine singular

Examples:

• un paper
• una resposta

This is why the sentence has un paper but later la resposta.

In this sentence, un paper usually means a piece/sheet of paper or a paper/note, not the material in an abstract sense.

So depending on context, it could suggest:

• a sheet of paper
• a note
• a document

If you were talking about paper as a material in general, Catalan can also use paper, but the context would make that clear.

La resposta means the answer, referring to a specific answer.

Catalan often uses the definite article where English also uses it:

• amb la resposta = with the answer

If you said amb resposta, it would sound incomplete or unusual here, because it would mean something more like with answer rather than with the answer.

Here amb means with.

• un paper amb la resposta = a paper with the answer

It does not mean and in standard Catalan.
A learner might confuse it with Spanish ambos or with other small connecting words, but in Catalan amb is a preposition meaning with.

Al costat de means next to, beside, or at the side of.

In this sentence:

• al costat de l'ordinador = next to the computer

It is a fixed expression:

• costat = side
• de = of
• al = a + el = to the / at the

Literally, it is something like at the side of the computer, but in natural English we usually say next to the computer.

Because two different grammar things are happening:

1. al is a contraction of a + el

   • a el costat becomes al costat

2. l'ordinador is the article el shortened before a vowel

   • el ordinador becomes l'ordinador

So:

• al costat de l'ordinador

breaks down as:

• a + el costat
• de + l'ordinador

This is very common in Catalan.

Because ordinador begins with a vowel, and the masculine singular article el is usually shortened to l' before a vowel sound.

So:

• el llibre
• l'ordinador
• l'amic

This is similar to how French shortens articles before vowels.

Yes, it is completely normal.

The structure is:

• Hi ha = there is
• un paper = a paper
• amb la resposta = with the answer
• al costat de l'ordinador = next to the computer

Catalan often puts descriptive phrases after the noun:

• un paper amb la resposta
• un home amb ulleres
• una noia de Barcelona

So the sentence flows in a very natural Catalan order.

Yes, but it would mean something slightly different in focus.

• Hi ha un paper amb la resposta... focuses first on the paper
• Hi ha la resposta en un paper... focuses more on the answer

The original sentence is more natural if you are pointing out the existence of a paper/note that has the answer on it.

You would make the noun phrase plural, but hi ha usually stays the same.

Examples:

• Hi ha uns papers al costat de l'ordinador.
• Hi ha dos papers amb les respostes al costat de l'ordinador.

Notice:

• un paper → uns papers
• la resposta → les respostes
• hi ha stays hi ha

A careful approximate pronunciation is:

ee AH oom puh-PAYR ahm lah rəs-PO-stuh ahl koo-STAT duh lur-dee-nuh-DOHR

A few useful notes:

• hi ha sounds roughly like ee AH
• paper in Catalan is stressed on the second syllable: pa-PER
• resposta has stress on pos
• costat has stress on the last syllable
• ordinador has stress on the last syllable: or-di-na-DOR

Exact pronunciation varies a bit by dialect, but this will help you recognize the sentence.

A native English speaker should especially notice these:

• hi ha = there is / there are
• noun gender:
  • un paper masculine
  • la resposta feminine
• amb = with
• al costat de = next to
• article changes:
  • a + el = al
  • el + ordinador = l'ordinador

So this one sentence is useful because it combines:

• existence (hi ha)
• articles
• gender
• a common prepositional expression
• contractions and elision