Se a secadora estiver ocupada, eu penduro a camisa no varal com um pregador.

Because Portuguese normally uses the future subjunctive after se when talking about a possible future situation.

So:

Se a secadora estiver ocupada... = if the dryer is occupied / if the dryer happens to be in use

This is the standard pattern for future conditions in Portuguese:

se + future subjunctive

Examples: Se chover, eu fico em casa.
Se ele chegar cedo, a gente sai.

If you say Se a secadora está ocupada, that usually sounds more like a present, real situation: If the dryer is occupied right now... It is not the best choice for a general future condition like the one in your sentence.

Estiver is the future subjunctive form of estar.

The verb estar is irregular, so this form does not look like the infinitive very much. Some useful forms are:

quando eu estiver
se eu estiver
quando ela estiver
se a secadora estiver

This tense is very common in Portuguese after words like:

se = if
quando = when
assim que = as soon as

Examples: Quando eu estiver pronto, eu aviso.
Se ele estiver cansado, ele não vem.

In Portuguese, the present tense is often used for a habitual action or a normal response to a situation.

So:

Se a secadora estiver ocupada, eu penduro a camisa...

can mean something like:

If the dryer is busy, I hang the shirt...
in the sense of that is what I do.

It sounds natural because the sentence describes a routine or standard reaction.

You could also say:

Se a secadora estiver ocupada, eu vou pendurar a camisa...
This sounds a bit more like one future event.

Pendurarei is correct, but it is more formal and less common in everyday spoken Brazilian Portuguese.

Because ocupada agrees with secadora, and secadora is a feminine noun.

In Portuguese, adjectives usually match the noun in gender and number:

o secador ocupado
a secadora ocupada

So the ending changes: -o for masculine
-a for feminine

Here, ocupada means occupied, busy, or in use.

Yes. Secadora is a normal and natural way to say dryer, especially a clothes dryer.

Depending on context, Brazilians may also say:

secadora de roupas = clothes dryer
máquina de secar = drying machine

But secadora alone is very common if the context is laundry.

No is a contraction of:

em + o = no

So:

no varal = on the clothesline / on the drying line

This kind of contraction is extremely common in Portuguese:

em + a = na
em + os = nos
em + as = nas

Examples: na casa = in the house
no carro = in the car
nos armários = in the closets

So no varal literally comes from em o varal, but native speakers do not say it that way.

Varal is a clothesline or a place where clothes are hung to dry.

In Brazil, it can refer to:

• a traditional line for hanging clothes
• an indoor drying rack
• another structure used for air-drying laundry

So pendurar a camisa no varal means to hang the shirt up to dry.

Here, pregador means a clothespin or clothes peg.

In Brazil, you may also hear:

prendedor de roupa = clothespin
pregador de roupa = clothespin

Pregador by itself can mean other things in other contexts, such as preacher, but in a laundry sentence with varal, the meaning is clearly clothespin.

So com um pregador means using a clothespin.

Portuguese uses definite articles more often than English.

So a camisa can mean:

• the shirt already known from context
• the shirt I am dealing with in this situation
• sometimes simply the item as part of the action

If you said uma camisa, that would emphasize one shirt or some shirt, often introducing it as less specific.

In many everyday situations, Portuguese prefers a camisa, o carro, a porta, where English might simply say the shirt, or sometimes even no article at all.

Yes. Brazilian Portuguese often allows the subject pronoun to be omitted when the verb already makes the subject clear.

So this is also natural:

Se a secadora estiver ocupada, penduro a camisa no varal com um pregador.

The -o ending in penduro already shows that the subject is I.

Keeping eu is also fine. It can add:

• emphasis
• contrast
• clarity

For example, eu may sound more explicit if you want to stress that I do it.

You can, but it changes the feel.

Se a secadora estiver ocupada is the normal choice for:

• a future possibility
• a general condition
• a rule or usual response

Se a secadora está ocupada sounds more like:

• a present factual situation
• the dryer is occupied right now

So if you are saying what you usually do whenever that situation happens, estiver is the better choice.

Yes. Com um pregador tells you how the shirt is hung: with a clothespin. It goes with the action penduro.

The original order is very natural:

eu penduro a camisa no varal com um pregador

Portuguese word order is somewhat flexible, and you could also hear:

eu penduro a camisa com um pregador no varal

But that version can sound slightly less neat, because no varal and com um pregador are both modifying the action. Keeping no varal first and com um pregador after it is clear and natural in this sentence.