Das Handtuch ist noch feucht, darum lege ich es auf den Balkon.

Because Handtuch is a neuter noun in German.

• das Handtuch = the towel
• A neuter noun is later referred to with es = it

So:

• Das Handtuch ist noch feucht.
• Darum lege ich es auf den Balkon.

This is the same kind of agreement English has with the towel ... it, but in German the pronoun choice depends on the noun’s grammatical gender.

Because feucht is a predicate adjective here, not an adjective directly in front of a noun.

Compare:

• das feuchte Handtuch = the damp towel
  
  • here the adjective is before the noun, so it takes an ending
• Das Handtuch ist feucht = The towel is damp
  
  • here the adjective comes after ist and stays in its basic form

After verbs like sein, werden, and bleiben, adjectives usually do not take endings.

Here noch means still.

So Das Handtuch ist noch feucht means The towel is still damp.

It suggests that the towel has not dried yet. In other contexts, noch can also mean things like:

• yet
• another
• more

But in this sentence, still is the natural meaning.

Darum means therefore, for that reason, or that’s why.

It connects the two ideas:

• the towel is still damp
• because of that, I put it on the balcony

So the logic is:

• Das Handtuch ist noch feucht
• darum lege ich es auf den Balkon

Very common English equivalents are:

• therefore
• so
• that’s why
• for that reason

Because German main clauses follow the verb-second rule.

That means the finite verb must be in the second position of the clause. If darum comes first, the verb must come next:

• Darum lege ich es auf den Balkon.

Structure:

• position 1: darum
• position 2: lege
• then: ich es auf den Balkon

This is a very important German pattern:

• Heute gehe ich nach Hause.
• Dann rufe ich dich an.
• Darum lege ich es auf den Balkon.

If you start with something other than the subject, the verb still stays in second position, and the subject moves after the verb.

Because the pronoun refers to das Handtuch, which is neuter.

German accusative pronouns are:

• ihn for masculine nouns
• sie for feminine nouns
• es for neuter nouns

Since Handtuch is neuter, the correct pronoun is es.

So:

• Ich lege das Handtuch auf den Balkon.
• Ich lege es auf den Balkon.

Because auf is a two-way preposition. With these prepositions, German uses:

• accusative for direction/movement toward a destination
• dative for location/no movement

Here, the towel is being moved to the balcony, so German uses the accusative:

• auf den Balkon = onto/to the balcony

Compare:

• Ich lege es auf den Balkon.
  Movement → accusative
• Es liegt auf dem Balkon.
  Location → dative

Also note:

• der Balkon is masculine
• accusative masculine of der is den
• dative masculine of der is dem

Legen usually means to lay or to put something down in a lying position.

German often uses more specific placement verbs than English:

• legen = lay something down
• stellen = stand something up
• setzen = set someone/something into a sitting position
• hängen = hang something

So lege ich es auf den Balkon suggests placing the towel down somewhere, probably flat or at least not upright.

In everyday English, we often just say put, but German often chooses a more precise verb.

Yes, it is normal and correct here.

The sentence contains two main clauses:

• Das Handtuch ist noch feucht
• darum lege ich es auf den Balkon

In standard written German, when two independent clauses are connected like this with darum, a comma is normally used to separate them clearly.

So the punctuation in the sentence is standard:

• Das Handtuch ist noch feucht, darum lege ich es auf den Balkon.

Yes. In this sentence, darum, deshalb, and deswegen are all very similar.

You could say:

• Das Handtuch ist noch feucht, darum lege ich es auf den Balkon.
• Das Handtuch ist noch feucht, deshalb lege ich es auf den Balkon.
• Das Handtuch ist noch feucht, deswegen lege ich es auf den Balkon.

All of these mean roughly The towel is still damp, so/therefore I’m putting it on the balcony.

There can be small differences in style or frequency depending on region and context, but for most learners they are close enough to treat as near-synonyms here.

Yes, darum can sometimes literally relate to around that/about that, depending on context, but that is not what it means here.

In this sentence, darum clearly functions as a connector meaning therefore / for that reason.

You can tell from the structure:

• first clause: The towel is still damp
• second clause: for that reason, I put it on the balcony

So here darum is not spatial or literal; it is logical and means that’s why.

Yes, but the meaning changes slightly.

• feucht = damp, moist
• nass = wet

So:

• Das Handtuch ist noch feucht suggests the towel is not completely dry yet
• Das Handtuch ist noch nass suggests it is wetter than that

For a towel that is drying but not dry yet, feucht is often a very natural choice.