Sebelum minum obat, saya mengisi gelas ini dengan air hangat.

Because that phrase gives the time context first: before taking/drinking medicine.

In Indonesian, a time expression like this can come at the beginning of the sentence, just like English Before taking medicine, .... It helps set the scene before the main action.

You could also place the main clause first and move the time clause later:

Saya mengisi gelas ini dengan air hangat sebelum minum obat.

That is also natural.

In Indonesian, the subject is often left out if it is already clear from context.

Here, the main clause has saya, so the listener naturally understands that the person who will minum obat is also saya.

So both are possible:

• Sebelum minum obat, saya mengisi gelas ini dengan air hangat.
• Sebelum saya minum obat, saya mengisi gelas ini dengan air hangat.

The version without the second saya sounds more efficient and natural in many contexts.

Yes, literally it is drink medicine, but in normal Indonesian it often corresponds to English take medicine.

So minum obat is a very common expression for taking oral medicine, even if English would not always use drink in the same situation.

A learner should remember it as a set phrase:

• minum obat = take medicine

Because mengisi is the normal active transitive verb form here.

The base/root is isi, meaning something like contents or fill/content.
With the prefix meN-, it becomes mengisi, meaning to fill.

So:

• isi = root/base
• mengisi = to fill

In this sentence, saya is actively doing something to gelas ini, so mengisi is the expected form.

It comes from the prefix meN- plus the root isi.

When meN- is added to a root beginning with a vowel like i-, it commonly appears as meng-:

• isi → mengisi

This is a very common Indonesian pattern. The spelling may look surprising at first, but it is completely regular.

In Indonesian, demonstratives like ini and itu usually come after the noun.

So:

• gelas ini = this glass
• obat itu = that medicine

This is the normal Indonesian word order.

Because adjectives usually come after the noun in Indonesian.

So:

• air hangat = warm water
• teh panas = hot tea
• rumah besar = big house

This is one of the most important word-order differences from English.

Here dengan means with, in the sense of what the glass is being filled with:

• mengisi gelas ini dengan air hangat
• fill this glass with warm water

In other contexts, dengan can also mean using, by, or together with, so its meaning depends on the sentence.

In this sentence, it clearly introduces the substance inside the glass.

Yes—this is a classic false friend.

In Indonesian:

• air = water

The Indonesian word is not the same as the English word in meaning, even though it is spelled the same way.

So:

• air hangat = warm water
• not warm air

This is a word learners usually need to memorize early.

Indonesian does not have articles like English a/an and the.

Meaning is usually understood from context.

So:

• obat can mean medicine, the medicine, or some medicine, depending on context.
• gelas ini is already specific because ini means this, so you do not need a separate word for the.

The comma separates the introductory time clause from the main clause.

So the structure is:

• Sebelum minum obat, = introductory clause
• saya mengisi gelas ini dengan air hangat. = main clause

This is similar to English punctuation in sentences like:

• Before taking medicine, I fill this glass with warm water.

Yes, but the meaning changes.

• air hangat = warm water
• air panas = hot water

So in this sentence, air hangat suggests water that is pleasantly warm, not very hot. That is probably why it was chosen.

Gelas usually means a drinking glass or tumbler.
Cangkir usually means a cup, especially one with a handle.

So if the sentence says gelas ini, the image is more likely a glass than a mug or teacup.