Si la etiqueta dice que la prenda no se puede planchar, es mejor llevarla a la lavandería.

Si means if and introduces a condition:

Si la etiqueta dice... = If the label says...

This is a very common pattern in Spanish:

• Si hace frío, me pongo un abrigo.
• Si tienes tiempo, llámame.

In this sentence, both verbs are in the present because it expresses a real, general situation: if the label says that, then this is the best thing to do.

Que means that and links the two parts of the sentence.

• La etiqueta dice = The label says
• que la prenda no se puede planchar = that the garment cannot be ironed

So:

La etiqueta dice que... = The label says that...

Just like in English, Spanish often uses que after verbs like decir, pensar, creer, etc.

• Dice que viene mañana. = He/She says that he/she is coming tomorrow.

In English, that is often optional, but in Spanish que is normally required here.

Prenda means garment or item of clothing.

It is a fairly general word for a piece of clothing. In everyday Spanish, people might also say more specific words like:

• camisa = shirt
• pantalones = trousers
• jersey = jumper/sweater

But on labels, in instructions, or in more neutral/formal language, prenda is very common.

So la prenda here means the garment/item of clothing being referred to on the label.

This is one of the most useful structures in Spanish.

No se puede planchar literally looks like it cannot be ironed / one cannot iron it.

The key parts are:

• se: used here in a passive or impersonal way
• puede: can
• planchar: to iron

So the whole idea is:

la prenda no se puede planchar = the garment cannot be ironed

This is a very natural way to express instructions or general rules in Spanish:

• No se puede fumar. = Smoking is not allowed.
• Se vende fruta. = Fruit is sold.
• Esta camisa se lava a mano. = This shirt is washed by hand.

Because la prenda is singular.

In this kind of se construction, the verb agrees with the thing affected:

• La prenda no se puede planchar.
• Las prendas no se pueden planchar.

So if the noun changes to plural, the verb changes too:

• La camisa se puede lavar.
• Las camisas se pueden lavar.

That is a good clue that this behaves a lot like a passive structure.

Because after poder you use an infinitive.

• puede planchar
• puede lavar
• puede usar

This is the same as in English:

• can iron
• can wash
• can use

So:

no se puede planchar = cannot be ironed / cannot be ironed by one / one cannot iron it

Es mejor + infinitive means it is better to + verb.

So:

• Es mejor llevarla... = It is better to take it...

This is a very common structure:

• Es mejor esperar. = It is better to wait.
• Es mejor no decir nada. = It is better not to say anything.

Spanish often uses the infinitive after expressions like es mejor, just as English uses to + verb.

Because la replaces la prenda to avoid repetition.

• llevar = to take
• la = it (referring to la prenda)

So:

llevarla = to take it

Spanish often attaches object pronouns to infinitives:

• lavarla = to wash it
• comprarlo = to buy it
• decirlo = to say it

You could also say es mejor llevar la prenda a la lavandería, but llevarla sounds more natural because la prenda was just mentioned.

In Spanish, when the verb is an infinitive, object pronouns can be attached directly to it.

So:

• llevar + la → llevarla

This is completely normal with infinitives:

• quiero verlo = I want to see it
• prefiero comprarla = I prefer to buy it
• es mejor guardarlo = it is better to keep it

In this sentence, attaching the pronoun is the standard and natural choice.

Because llevar takes a when you say where something is being taken.

• llevar algo a algún sitio = to take something to somewhere

So:

• llevarla a la lavandería = to take it to the laundry/launderer

The la before lavandería is just the normal feminine singular article, because lavandería is a feminine noun.

Compare:

• llevarlo al médico = to take him/it to the doctor
• llevarla a casa = to take her/it home

It usually means laundry or laundry service, and depending on context it can be understood as a place where clothes are professionally washed/treated.

In Spain, tintorería is often the more specific word for dry cleaner.

So in real life, depending on the garment and the problem, a Spanish speaker might also say:

• llevarla a la tintorería

But in your sentence, lavandería is perfectly understandable as a place where you take clothes for professional care.

Yes, la prenda no puede plancharse is also possible.

Compare:

• la prenda no se puede planchar
• la prenda no puede plancharse

Both mean essentially the same thing: the garment cannot be ironed.

The version in your sentence, no se puede planchar, is extremely common and very natural, especially in instructions and general statements.

It is neutral and natural Spanish.

Some parts sound slightly more formal or instructional, especially:

• la prenda
• la etiqueta dice que...

That makes sense, because the context is clothing care instructions.

In more casual speech, someone might say something like:

• Si pone que no se puede planchar, mejor llévala a la lavandería.

But your sentence is completely standard and natural, especially in written or careful spoken Spanish.