A sapatilha está molhada depois da chuva.

In Portugal, sapatilha usually refers to a light shoe, often a trainer/sneaker. In some contexts it can also mean a ballet flat or similar soft shoe.

In this sentence, it is singular, so it means one shoe. If you meant a pair, you would normally say As sapatilhas estão molhadas.

A is the feminine singular definite article, meaning the.

So:

• a sapatilha = the shoe / the sneaker

If you wanted a shoe / a sneaker, you would say uma sapatilha.

Portuguese nouns have grammatical gender. Sapatilha is simply a feminine noun, so it takes feminine words with it:

• a sapatilha
• molhada

This is grammatical gender, not biological gender.

Because adjectives in Portuguese usually agree with the noun they describe.

Since sapatilha is feminine singular, the adjective must also be feminine singular:

• masculine singular: molhado
• feminine singular: molhada
• masculine plural: molhados
• feminine plural: molhadas

So:

• A sapatilha está molhada
• O sapato está molhado
• As sapatilhas estão molhadas

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

Here, está is used because being wet is a temporary condition or current state:

• A sapatilha está molhada = the shoe is wet right now

Using é here would sound wrong or very unnatural, because it would suggest that being wet is a permanent or defining characteristic.

The accent in está shows the stress and helps distinguish it from other forms.

It is stressed on the last syllable:

• es-TÁ

It also helps distinguish it from esta, which means this (feminine):

• esta sapatilha = this shoe
• está molhada = is wet

It literally means after the rain.

Breakdown:

• depois = after
• da = de + a
• chuva = rain

So da chuva means of the rain / the rain, and the full phrase is after the rain.

Because in Portuguese, de + a normally contracts to da.

So:

• de + a chuva → da chuva

This kind of contraction is very common in Portuguese.

Other examples:

• de + o = do
• em + a = na
• em + o = no

Its main meaning is time: after the rain.

However, in a sentence like this, it often also suggests the reason the shoe is wet. So a listener will probably understand that the rain caused it.

If you want to make the cause more explicit, you could say:

• A sapatilha está molhada por causa da chuva.
  = The shoe is wet because of the rain.

Yes, if you are talking about one shoe.

English speakers sometimes think of footwear as a pair, but Portuguese can refer to just one item very naturally:

• A sapatilha está molhada = one shoe is wet
• As sapatilhas estão molhadas = both shoes are wet

So the singular is fine if that is what you mean.

Yes. You can move the time phrase to the front:

• Depois da chuva, a sapatilha está molhada.

This is also correct. The meaning stays basically the same, but the sentence now puts more emphasis on when/under what circumstances.

A rough pronunciation guide is:

• sapatilha ≈ suh-puh-TEE-lyuh
• molhada ≈ moh-LYA-duh or moh-LYA-dah depending on how carefully it is said

The important sound here is lh, which is a special Portuguese sound. It is similar to the lli sound in some pronunciations of million, though not exactly the same.

So both of these words contain that lh sound:

• sapati-lha
• mo-lha-da