Mereka belajar tentang angkasa.

Mereka means they when talking about people. It does not show gender, so it can refer to men, women, or a mixed group.

A useful point: mereka is normally used for people, not for things or animals in the way English they can be.

Belajar can mean both learn and study, depending on context.

In this sentence, it is most naturally understood as study or are learning:

• Mereka belajar tentang angkasa. = They are studying/learning about space.

Malay often uses the same verb where English might choose either learn or study.

Tentang means about.

So:

• belajar tentang angkasa = study/learn about space

This is a very common pattern in Malay:

• belajar tentang sejarah = study about history
• belajar tentang haiwan = learn about animals

If you leave out tentang, the sentence may sound incomplete or unnatural in this meaning. Another possible way to express the idea is:

• Mereka mempelajari angkasa. = They study space.

That version is a bit more formal or bookish.

Angkasa means space, especially in the sense of outer space.

Sometimes you may also see:

• ruang angkasa = outer space

Both can refer to space, but ruang angkasa is a little more explicit. In many contexts, angkasa by itself is perfectly natural.

Malay does not usually need a separate word like English am / is / are in sentences like this.

So:

• Mereka belajar tentang angkasa.

already means:

• They study about space
• They are studying about space
• They learn about space

The exact time is usually understood from context, or from time words if they are added, such as:

• sekarang = now
• semalam = yesterday
• esok = tomorrow

Strictly speaking, Malay verbs do not change form for tense the way English verbs do.

Belajar stays belajar whether the action is present, past, or future, unless something in the sentence shows the time:

• Mereka belajar tentang angkasa. = They study / are studying about space.
• Semalam mereka belajar tentang angkasa. = Yesterday they studied about space.
• Esok mereka akan belajar tentang angkasa. = Tomorrow they will study about space.

So in the original sentence, the present-time meaning comes from context, not from verb conjugation.

The word order is very straightforward:

• Mereka = subject
• belajar = verb
• tentang angkasa = prepositional phrase

So the pattern is:

• Subject + Verb + Prepositional phrase

This is similar to English:

• They study about space.

No. Because tentang angkasa means about space, not in space.

If you want to say in space, you would use di angkasa:

• Mereka belajar tentang angkasa. = They study about space.
• Mereka belajar di angkasa. = They study in space.

So tentang and di give very different meanings.

Malay does not use articles like English a, an, and the in the same way.

So angkasa can simply mean space without needing a separate word for the.

Whether English should use space, the space, or outer space depends on translation style and context, but Malay does not have to mark that distinction here.

In many contexts, Malay can drop subjects if the meaning is already clear from context.

So if everyone already knows who is being talked about, a speaker might simply say:

• Belajar tentang angkasa.

But in a normal full sentence, especially for learners, keeping mereka is best:

• Mereka belajar tentang angkasa.

It makes the sentence complete and clear.