La nena juga a terra, al costat de la cortina.

La nena uses the definite article la, so it means the girl.

Catalan often uses articles in places where English might also use one, but sometimes Catalan uses them a bit more regularly. In this sentence, la nena is simply the normal way to say the girl.

• la = the
• nena = girl, little girl

Also, nena usually suggests a child, not an adult woman.

Juga is the 3rd person singular present indicative of jugar (to play).

So:

• jo jugo = I play
• tu jugues = you play
• ell / ella juga = he / she plays

In this sentence, La nena juga... means The girl plays... or, depending on context, The girl is playing... Catalan present tense often covers both the simple present and the present continuous idea.

Because a terra is a very common fixed expression in Catalan meaning on the ground or on the floor.

Here, terra does not take an article. So:

• a terra = on the floor / on the ground

This is one of those expressions you should learn as a chunk.

Compare:

• seure a terra = to sit on the floor
• caure a terra = to fall to the ground
• jugar a terra = to play on the floor

So the a here is part of the location expression a terra, not a contraction with an article.

It can mean all of those, depending on context.

Common meanings of terra include:

• earth/soil/land
• ground
• floor

In this sentence, because we have la cortina (the curtain), the setting is probably indoors, so a terra is most naturally understood as on the floor.

So Catalan uses the same word where English often distinguishes between ground and floor.

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

It is a very common Catalan expression:

• al costat de la cortina = next to the curtain

Literally, it is something like:

• al = at the
• costat = side
• de = of

So the whole phrase literally resembles at the side of, but in natural English we usually say next to or beside.

Al is a contraction of a + el.

So:

• a
  • el = al

In this sentence:

• al costat = a el costat = at the side

This contraction happens with masculine singular el.

A similar contraction is:

• de + el = del

For example:

• al parc = to the park / at the park
• del llibre = of the book / from the book

Because cortina is a feminine noun.

So:

• de + la = de la
• de + el = del

Since the noun is feminine:

• la cortina = the curtain
• al costat de la cortina = next to the curtain

You would only use del with a masculine singular noun:

• del llibre = of the book
• del cotxe = of the car

No, not really.

In jugar a futbol, the preposition is tied to what is being played:

• jugar a futbol = to play football
• jugar a cartes = to play cards

But in juga a terra, a terra is a location phrase:

• juga = plays
• a terra = on the floor

So here the a belongs to the expression a terra, not to the verb in the same way as in jugar a futbol.

That is an important distinction for learners.

Not necessarily. The sentence would also be natural without the comma:

La nena juga a terra al costat de la cortina.

The comma here helps separate the two location details:

• a terra = on the floor
• al costat de la cortina = next to the curtain

So the comma can make the sentence feel a little clearer or more rhythmic, but it is not essential in every context.

Yes, but it means something slightly different.

• La nena juga a terra... = The girl is playing on the floor...
• La nena està a terra... = The girl is on the floor...

So:

• juga focuses on the action of playing
• està focuses on her position or location

Both can be correct, but they do not mean exactly the same thing.

Because al costat de is a fixed expression in Catalan.

Catalan often forms location expressions with an article:

• al costat de = next to
• a la dreta de = to the right of
• a l’esquerra de = to the left of

So you should learn al costat de as a whole phrase, not try to build it word by word every time.

Not always. Nena usually refers to a young girl or little girl.

Some related words:

• nena = little girl / girl
• noia = girl, young woman
• dona = woman

So in this sentence, la nena suggests that the person is a child, which fits well with juga and the image of playing on the floor.