Adik laki-laki saya belum terbiasa memakai sumpit, jadi dia menjatuhkan sosis ke piringnya.

Adik means younger sibling, so by itself it does not specify male or female. Adding laki-laki makes it clear that the sibling is male: my younger brother.

In everyday Indonesian, people often just say adik saya if the gender is already obvious from context.

Belum means not yet, while tidak means not.

So belum terbiasa means not used to it yet, which suggests this may change in the future. That fits very well here: the younger brother has not become comfortable with chopsticks yet.

If you said tidak terbiasa, it would sound more like a general statement that he is not accustomed to it, without the strong yet idea.

Terbiasa means accustomed, used to, or familiar through habit.

It comes from biasa, which can mean usual, ordinary, or accustomed depending on context. In terbiasa, the ter- form gives a stative meaning here, so terbiasa memakai sumpit means accustomed to using chopsticks.

Yes, menggunakan would also work.

Both memakai and menggunakan can mean to use, but memakai is often a bit more everyday and natural in speech. With utensils, tools, and clothes, memakai is very common. So memakai sumpit sounds completely natural.

In normal usage, sumpit usually refers to chopsticks as the eating utensil, often understood as the pair.

If you really want to be specific, you can say sepasang sumpit for a pair of chopsticks. But in most sentences, just sumpit is enough.

Here jadi means so, therefore, or as a result.

It connects the first clause and the second clause:

• Adik laki-laki saya belum terbiasa memakai sumpit
• jadi dia menjatuhkan sosis ke piringnya

So the structure is basically He isn’t used to using chopsticks yet, so...

Because jatuh means to fall, while menjatuhkan means to drop something or to cause something to fall.

Compare:

• Sosis jatuh = The sausage fell
• Dia menjatuhkan sosis = He dropped the sausage

So menjatuhkan is the correct choice because the subject is causing the sausage to fall.

Ke usually marks movement toward a destination, while di marks location.

So ke piringnya focuses on the motion/result: the sausage went to/onto his plate.
If you said di piringnya, that would focus more on where the sausage was located.

In practice, Indonesian sometimes uses ke in places where English would naturally say onto.

Here -nya means his/her.

So piringnya means his plate in this context. Because the previous subject is dia, the listener naturally understands that -nya refers to that person.

Remember that -nya is not gender-specific, just like dia. It can mean his, her, or even their depending on context.

Using dia avoids repetition and sounds natural.

Indonesian often introduces someone with a full noun phrase and then refers back to them with dia in the next clause, just like English does with he or she. So this is a very normal pattern:

• Adik laki-laki saya ...
• jadi dia ...

Indonesian does not normally use articles like a, an, or the.

So sosis can mean a sausage, the sausage, or just sausage, depending on context. The listener figures it out from the situation rather than from an article.

That is very common in Indonesian nouns in general.