O seu casaco está no armário.

In European Portuguese, it is very common to use the definite article before a possessive:

• o seu casaco = your coat / his coat / her coat
• a minha casa = my house
• os nossos amigos = our friends

English usually does not do this, so it feels strange at first. For a learner, it helps to think of o seu casaco as the normal Portuguese way of saying your coat, not as the your coat.

That is a very common question, especially in European Portuguese.

In Portugal:

• teu / tua / teus / tuas usually go with tu (informal you)
• seu / sua / seus / suas usually go with você, o senhor, a senhora, or can mean his/her/their

So if you are speaking informally to a friend, O teu casaco está no armário is often more natural in Portugal.

O seu casaco está no armário is possible, but in European Portuguese it often sounds:

• more formal, or
• potentially ambiguous

Yes. Seu is ambiguous.

Depending on context, O seu casaco está no armário could mean:

• Your coat is in the wardrobe
• His coat is in the wardrobe
• Her coat is in the wardrobe

Because of that, Portuguese often uses other forms to make things clearer:

• O casaco dele está no armário = His coat is in the wardrobe
• O casaco dela está no armário = Her coat is in the wardrobe

This is especially useful when there could be confusion.

Portuguese uses estar for location:

• O seu casaco está no armário = the coat is located in the wardrobe

Use ser (é) for identity, definition, time, and similar ideas:

• Isto é um casaco. = This is a coat.
• O armário é grande. = The wardrobe is big.

So for saying where something is, estar is the normal verb.

No is a contraction of:

• em = in / on / at
• o = the (masculine singular)

So:

• em + o = no

That means:

• no armário = in the wardrobe / closet

Similar contractions are:

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

Because armário is a masculine noun.

In Portuguese, articles and some other words must match the noun’s gender:

• o armário = masculine
• therefore no armário

If the noun were feminine, you would use na:

• na caixa = in the box
• na mala = in the suitcase

Armário is a general word for a storage piece of furniture. Depending on context, it can mean:

• wardrobe
• closet
• cabinet
• cupboard

In this sentence, if the meaning shown is something like wardrobe or closet, that fits well.

So armário is broader than one single English word.

It can mean either, depending on context.

In European Portuguese, casaco is a fairly broad word for an outer garment. In English, the best translation might be:

• coat
• jacket
• sometimes even something like cardigan in certain contexts

So learners should not expect a perfect one-to-one match every time.

A rough learner-friendly pronunciation is:

u SEU kə-ZA-ku (i)sh-TA nu ar-MA-ryu

A few useful notes:

• O often sounds like a weak u
• seu is said as one syllable, roughly like say-oo said very quickly
• casaco has the stress on za
• está has the stress on the last syllable
• no often sounds like nu
• armário has the stress on má

European Portuguese reduces many unstressed vowels, so the sentence may sound more compressed than you expect.

The accents help show stress, and sometimes vowel quality.

• está → stress on the last syllable: es-TÁ
• armário → stress on má: ar-MÁ-rio

Without the accent, a learner might put the stress in the wrong place.

So accents in Portuguese are important: they are not optional decoration.

Yes, but O seu casaco está no armário is the most neutral and natural order.

It follows the basic pattern:

• subject: O seu casaco
• verb: está
• place: no armário

You can change the order for emphasis in some contexts, but that is less basic and often more marked. For example, Portuguese might move things around in speech for focus, but as a learner, the standard order is the safest choice.

Everything has to agree in gender and number.

Examples:

• Os seus casacos estão no armário. = Your coats are in the wardrobe.
• A sua camisa está no armário. = Your shirt is in the wardrobe.
• As suas camisas estão no armário. = Your shirts are in the wardrobe.

Notice the changes:

• o / a / os / as
• seu / sua / seus / suas
• está / estão

Agreement is a big part of Portuguese grammar.