На этикетке написано, что рубашку нельзя стирать в горячей воде.

Because на этикетке means on the label, and after на in the meaning of location, Russian usually uses the prepositional case.

• этикетка = label
• на этикетке = on the label

So:

• nominative: этикетка
• prepositional: на этикетке

This is the normal pattern for talking about where something is written or located.

Here написано is being used in an impersonal way: it is written / it says.

Even though этикетка is feminine, the sentence is not really focusing on the label as the grammatical subject. Russian often uses neuter singular short-form passive words like написано, сказано, указано in this impersonal sense.

So:

• На этикетке написано... = It says on the label...
• more literally: On the label, it is written...

If you said На этикетке написана инструкция, then написана would agree with инструкция because now there is a clear feminine noun being described.

Что here means that and introduces a subordinate clause.

So the structure is:

• На этикетке написано, что...
• It says on the label that...

Everything after что is the content of what is written on the label.

Because рубашку is in the accusative case, which is used for the direct object of стирать.

• рубашка = shirt (nominative, dictionary form)
• стирать рубашку = to wash a shirt

In the clause рубашку нельзя стирать, the shirt is the thing being washed, so it takes the accusative.

For feminine nouns ending in -а, the accusative singular usually changes to -у:

• рубашка → рубашку

Because Russian often expresses general rules without an explicit subject.

Нельзя + infinitive means:

• it is not allowed to...
• one must not...
• you cannot / should not... in a general sense

So рубашку нельзя стирать means something like:

• The shirt must not be washed
• You must not wash the shirt

The doer is left unspecified because this is a general instruction.

Here нельзя means must not, not allowed, or cannot in the sense of prohibition.

It is very common in instructions and rules:

• Нельзя курить. = No smoking.
• Здесь нельзя парковаться. = You must not park here.

In your sentence, нельзя is stronger than just it’s not a good idea. It gives the idea of a rule or prohibition from the washing instructions.

Because after нельзя, Russian often uses the imperfective infinitive when talking about a general prohibition or rule.

• стирать = to wash, to do washing
• постирать = to wash something once / to wash it completely

Laundry instructions are usually about what kind of action is generally permitted or forbidden, so the imperfective стирать is the natural choice:

• рубашку нельзя стирать в горячей воде = the shirt must not be washed in hot water

Using постирать would sound more like a single completed washing event, which is less natural in this context.

Because here в means in, describing the medium or location in which the washing happens, so Russian uses the prepositional case.

• вода = water
• prepositional: в воде = in water
• adjective agreement: горячая вода → в горячей воде

So:

• в горячей воде = in hot water

If you said в горячую воду, that would usually mean into hot water, showing movement into it. But this sentence is not about movement; it is about washing something in hot water.

Yes. It is a very direct match:

• в = in
• горячей = hot
• воде = water (prepositional case)

So the phrase means in hot water. In this sentence it refers to the temperature of the water used for washing.

The sentence is:

На этикетке написано, что рубашку нельзя стирать в горячей воде.

A natural breakdown is:

• На этикетке написано = It says on the label
• что = that
• рубашку нельзя стирать в горячей воде = the shirt must not be washed in hot water

Russian word order is flexible, but this order is very natural and neutral.

You could move things around for emphasis, for example:

• На этикетке написано, что в горячей воде рубашку нельзя стирать.

This still means the same thing, but it puts more emphasis on in hot water.

Grammatically, yes, but it would be less natural for a clothing label.

The given sentence:

• рубашку нельзя стирать в горячей воде

is the normal, idiomatic way to express washing instructions.

Something like:

• рубашка не должна стираться в горячей воде

is understandable, but it sounds heavier and less natural for everyday care instructions.

Russian often prefers:

• нельзя + infinitive
• especially in rules, signs, and instructions

Usually yes. Рубашка is the standard everyday word for shirt.

Depending on context, Russian can also use:

• сорочка — more formal, old-fashioned, or specific in some contexts
• футболка — T-shirt, not the same thing

For a normal shirt on a clothing label, рубашка is perfectly natural.