Meu cabelo está molhado, então vou ficar em casa.

In Portuguese, cabelo is very commonly used in the singular to mean hair in general.

So:

• Meu cabelo está molhado = My hair is wet

The plural cabelos is usually used when talking about:

• individual hairs
• different types/strands of hair
• a more descriptive or stylistic idea

Examples:

• Encontrei um cabelo na sopa. = I found a hair in the soup.
• Os cabelos dela são longos. = Her hair is long / Her hairs are long depending on context, though this sounds more descriptive/literary.

For everyday speech, meu cabelo is the normal way to say my hair.

Because cabelo is a masculine singular noun.

Possessives in Portuguese agree with the noun they describe:

• meu = my, masculine singular
• minha = my, feminine singular
• meus = my, masculine plural
• minhas = my, feminine plural

So:

• meu cabelo = my hair
• minha casa = my house
• meus livros = my books
• minhas roupas = my clothes

Even though the possessor is I, the possessive changes according to the noun, not according to the speaker.

For the same reason: molhado must agree with cabelo, which is masculine singular.

So the adjective changes to match the noun:

• cabelo molhado = wet hair
• camisa molhada = wet shirt
• sapatos molhados = wet shoes
• mãos molhadas = wet hands

In this sentence:

• Meu cabelo está molhado
• molhado matches cabelo

Portuguese has two main verbs for to be: ser and estar.

Here, estar is used because being wet is a temporary condition:

• Meu cabelo está molhado = My hair is wet right now

Using ser would sound wrong here, because it suggests a permanent or defining characteristic.

Compare:

• A água está fria. = The water is cold right now
• O gelo é frio. = Ice is cold by nature

So wetness in this sentence is a current state, not an essential quality.

Here, então means so, therefore, or in that case.

It connects the first idea to the result:

• Meu cabelo está molhado, então vou ficar em casa.
• My hair is wet, so I’m going to stay home.

It shows consequence.

A useful comparison:

• porque = because
• então = so / therefore

Examples:

• Vou ficar em casa porque meu cabelo está molhado. = I’m staying home because my hair is wet.
• Meu cabelo está molhado, então vou ficar em casa. = My hair is wet, so I’m staying home.

Same basic idea, but the structure changes.

Yes, vou literally means I go, but in Portuguese, ir + infinitive is a very common way to talk about the near future.

So:

• vou ficar = I am going to stay
• very naturally in English: I’ll stay / I’m going to stay

This is one of the most common future constructions in Brazilian Portuguese.

Compare:

• vou sair = I’m going to leave
• vou estudar = I’m going to study
• vou dormir = I’m going to sleep

There is also a simple future form:

• ficarei em casa

But in everyday Brazilian Portuguese, vou ficar em casa sounds much more natural and common.

Ficar is a very flexible verb. Here it means to stay or to remain.

So:

• vou ficar em casa = I’m going to stay home

Depending on context, ficar can also mean:

• to stay
• to remain
• to become
• to be located
• in some contexts, even to hook up with someone

Examples:

• Vou ficar em casa. = I’m going to stay home.
• Fiquei cansado. = I became tired.
• Onde fica o banco? = Where is the bank located?

In your sentence, the meaning is clearly stay.

Em casa is the normal expression for at home.

So:

• ficar em casa = stay at home

Portuguese treats this as a set expression.

Na casa means in/at the house, usually a specific house, often someone else’s house or a house that has been identified.

Compare:

• Estou em casa. = I’m at home.
• Estou na casa da minha amiga. = I’m at my friend’s house.
• Fiquei na casa dos meus pais. = I stayed at my parents’ house.

So if you mean home, use em casa.

Because Portuguese often drops subject pronouns when the verb ending already shows who the subject is.

• vou already means I go / I am going
• so (eu) vou can be just vou

That is why:

• Meu cabelo está molhado, então vou ficar em casa.

is perfectly natural.

You can include eu if you want emphasis, contrast, or extra clarity:

• Meu cabelo está molhado, então eu vou ficar em casa.

That might sound a bit more emphatic, like I’m the one who’s staying home or as for me, I’m staying home.

Yes. In spoken Brazilian Portuguese, tá is a very common short form of está.

So these both mean the same thing:

• Meu cabelo está molhado.
• Meu cabelo tá molhado.

The difference is mostly register:

• está = more neutral, careful, or formal
• tá = very common in everyday speech

If you are writing carefully, está is safer. If you are listening to Brazilians, you will hear tá all the time.

A rough pronunciation guide is:

meh-ooh kah-BEH-loh es-TAH mo-LYAH-doh, en-TAU voh fee-KAR en KAH-zah

A few helpful notes:

• meu sounds roughly like meh-ooh, but merged into one syllable
• lh in molhado is like the lli in million for many English speakers
• então ends with a nasal sound; it does not sound exactly like ow
• casa in Brazilian Portuguese usually has a z-like sound in the middle: KAH-zah

Pronunciation varies by region, but this will get you close.

Yes, it is natural and helpful here because então connects two clauses:

• Meu cabelo está molhado, então vou ficar em casa.

The comma marks the pause between:

1. the situation: Meu cabelo está molhado
2. the result: então vou ficar em casa

In informal writing, people are not always consistent with commas, but in standard writing this comma is a good choice.