Depois do jantar, ela passa a esfregona com água quente.

Because de + o contracts to do in Portuguese.

• de = of / from / after in some expressions
• o jantar = the dinner / dinner

So:

• de o jantar → do jantar

This kind of contraction is very common in Portuguese:

• de + a → da
• de + os → dos
• de + as → das

In depois do jantar, the whole phrase means after dinner.

The comma separates the time expression from the main clause.

• Depois do jantar = a time phrase
• ela passa a esfregona com água quente = the main statement

So the comma works a lot like in English:

• After dinner, she mops with hot water.

In short, the comma is natural and correct here, especially because the sentence begins with a longer introductory phrase.

Literally, passar a esfregona is something like to pass the mop. But in real usage, it means to mop the floor.

This is a very common kind of expression in Portuguese: a verb plus an object gives a meaning that English expresses differently.

So:

• Ela passa a esfregona = She mops / She runs the mop over the floor

You should learn passar a esfregona as a set phrase, not by translating each word separately every time.

Because esfregona is a feminine noun, and Portuguese often uses the definite article where English would not.

• a esfregona = the mop

In this expression, the article is part of the normal idiomatic phrase:

• passar a esfregona

Portuguese uses articles more often than English, so even when English says just mop, Portuguese may prefer a esfregona.

Yes, esfregona is standard and very common in European Portuguese for mop.

This matters because vocabulary can differ between European and Brazilian Portuguese. A learner focusing on Portugal should definitely know esfregona.

So this sentence sounds natural for Portugal.

Passa is the 3rd person singular present of passar:

• eu passo
• tu passas
• ele/ela passa

In this sentence, the present tense usually expresses a habitual action:

• Depois do jantar, ela passa a esfregona...
• After dinner, she mops... / she usually mops...

So it is not necessarily happening right now. It can describe a routine or regular habit.

Usually, by itself, this sentence is more naturally understood as a habit or general routine.

If you want to emphasize an action happening right now in European Portuguese, you would often use:

• Ela está a passar a esfregona. = She is mopping.

So:

• ela passa a esfregona = she mops / she usually mops
• ela está a passar a esfregona = she is mopping right now

It tells you how she mops: with hot water.

So the structure is:

• ela passa a esfregona
• com água quente

Together:

• She mops using hot water.

Grammatically, com água quente is a prepositional phrase introduced by com (with).

It describes the means or material involved in the action.

The adjective is already feminine: quente.

Some Portuguese adjectives have the same form for masculine and feminine:

• quente = hot
• grande = big
• interessante = interesting

So:

• água quente = hot water
• chá quente = hot tea

The adjective agrees in number, and sometimes in gender, but with quente the masculine and feminine singular forms look the same.

Because com água quente can mean with hot water in a general sense, not necessarily with the hot water.

Portuguese often omits the article in this kind of phrase when speaking generally about a substance or material.

Compare:

• com água quente = with hot water
• com a água quente = with the hot water

The version in your sentence is the more natural general one.

Yes, it is very normal and natural.

• depois de = after
• o jantar = dinner
• depois do jantar = after dinner

You will see the same pattern with other meals and events:

• depois do almoço = after lunch
• depois da aula = after class
• depois do trabalho = after work

It is one of the most useful everyday time expressions.

Yes. Portuguese often drops subject pronouns when the verb form already makes the subject clear.

So both are possible:

• Depois do jantar, ela passa a esfregona com água quente.
• Depois do jantar, passa a esfregona com água quente.

The version with ela may be used for clarity, emphasis, or contrast.

For example:

• O João lava a loiça, mas ela passa a esfregona.

Here ela helps stress that she, not someone else, does the mopping.

To some extent, yes. The given sentence is very natural, but Portuguese allows some variation.

Natural possibilities include:

• Depois do jantar, ela passa a esfregona com água quente.
• Ela passa a esfregona com água quente depois do jantar.

The first one emphasizes the time first. The second one sounds a bit more neutral in flow.

Both are correct, but starting with Depois do jantar is especially common when setting the scene or describing a routine.