O forno cerâmico está muito quente.

In Portuguese, a singular countable noun usually needs a determiner, such as an article.

So forno by itself often sounds incomplete, while o forno means the oven.

• o forno = the oven
• um forno = an oven

Here, o tells you we are talking about a specific oven.

Because forno is a masculine noun in Portuguese. Nouns have grammatical gender, and you usually have to learn it with the word.

That is why it takes:

• o forno in the singular
• os fornos in the plural

A useful habit is to learn nouns together with their article:

• o forno, not just forno

Because cerâmico is an adjective describing forno, and adjectives normally agree with the noun in gender and number.

Since forno is masculine singular, the adjective is also masculine singular:

• o forno cerâmico

Compare:

• o forno cerâmico = masculine singular
• a peça cerâmica = feminine singular
• os fornos cerâmicos = masculine plural
• as peças cerâmicas = feminine plural

In Portuguese, adjectives often come after the noun, much more often than in English.

So English ceramic oven becomes:

• forno cerâmico

Putting the adjective after the noun is the most normal order here.

In some cases, Portuguese adjectives can go before the noun, but that often changes the tone, emphasis, or meaning. For this sentence, forno cerâmico is the natural choice.

Portuguese has two verbs that both mean to be:

• ser
• estar

Here, está is used because muito quente describes a state or condition: the oven is hot right now.

So:

• O forno cerâmico está muito quente. = it is very hot at the moment

If you used é, it would sound more like you were describing an inherent characteristic, which does not fit as well here.

A common rule of thumb:

• ser = more permanent or defining
• estar = more temporary or current

Because here muito is an adverb, not an adjective.

It modifies quente, meaning very hot.

• muito quente = very hot

As an adverb, muito does not change to match gender or number.

Compare:

• muito quente = very hot
• muito alta = very tall
• muito interessantes = very interesting

But when muito is an adjective or determiner meaning much / many, it does change:

• muito calor = a lot of heat
• muita água = a lot of water
• muitos livros = many books
• muitas casas = many houses

Quente is one of those adjectives that has the same form for masculine and feminine singular.

So you get:

• o forno está quente
• a sopa está quente

The singular form stays quente for both genders.

Only the plural changes:

• os fornos estão quentes
• as sopas estão quentes

The accents mainly show stress.

• cerâmico is stressed on râ
• está is stressed on the final tá

So the stress is:

• ce-RÂ-mi-co
• es-TÁ

The accents help you avoid stressing the wrong syllable.

In European Portuguese, they can also help signal vowel quality, but for a learner the most useful first step is: they tell you where the stress goes.

A careful learner-friendly approximation is:

• u FOR-nu se-RÂ-mi-ku es-TÁ MUY-tu KEN-tuh

But in real European Portuguese, some unstressed vowels get reduced a lot, so it may sound closer to:

• u FOR-nu s'rÂ-mi-ku shtÁ MUY-tu KENT

A few important points:

• o in forno sounds more like oo than English or
• the r in forno is a tapped r
• the unstressed e in está is often very weak in Portugal
• final unstressed vowels are often reduced, especially in European Portuguese

So do not worry if native speakers seem to say less than what you see written.

This order is the normal one:

• O forno cerâmico está muito quente.

You can change parts of a Portuguese sentence for emphasis, but this is the neutral, standard structure:

• article + noun + adjective + verb + adverb + adjective

Also, muito normally comes before the adjective it modifies:

• muito quente
• not normally quente muito

So for everyday use, keep the sentence exactly in this order.

It would become:

• Os fornos cerâmicos estão muito quentes.

Notice all the agreement changes:

• o → os
• forno → fornos
• cerâmico → cerâmicos
• está → estão
• quente → quentes

But muito stays the same, because it is still an adverb.

Yes. Depending on context, cerâmico can mean:

• made of ceramic
• related to ceramics
• used for ceramics

So forno cerâmico could refer to a ceramic oven, or in some contexts something like a kiln used in ceramic work.

Usually the surrounding context makes the meaning clear. Grammar-wise, though, the structure stays the same: noun + adjective.