Há poeira na mesa, então eu passo um pano nela.

Yes. In this sentence, há means there is / there are.

• Há poeira na mesa = There is dust on the table

This use comes from the verb haver, which often expresses existence.

A very common spoken alternative in Brazilian Portuguese is:

• Tem poeira na mesa

That is extremely common in everyday speech, even though há is often presented in textbooks as the more formal or more traditionally grammatical option for there is/are.

Because poeira here is being used as an uncountable noun, like dust in English.

So:

• Há poeira na mesa = There is dust on the table

You would not normally say uma poeira in this context, just like you usually would not say a dust in English.

If you add something like an adjective or a more specific idea, other structures may appear, but in this basic sentence, plain poeira is the natural choice.

Na mesa means on the table.

It is formed from:

• em = in / on / at
• a = the

These combine into the contraction:

• em + a = na

So:

• na mesa = on the table

Other similar contractions:

• no = em + o
• nas = em + as
• nos = em + os

Yes, it can usually be omitted.

Portuguese often leaves out subject pronouns when the verb ending already makes the subject clear.

So both of these are natural:

• Então eu passo um pano nela
• Então passo um pano nela

Including eu can add clarity, emphasis, or contrast. For example, if you want to stress that I am the one doing it, eu makes that more explicit.

Passo is the present tense of passar for eu:

• eu passo = I pass / I wipe / I run

In this sentence, the present tense can express a habitual or typical action:

• There is dust on the table, so I wipe it with a cloth

It may sound a little like when that happens, this is what I do.

If you wanted a one-time past action, you would say something like:

• Havia poeira na mesa, então eu passei um pano nela
  = There was dust on the table, so I wiped it with a cloth

Passar um pano literally means to pass a cloth, but in natural English it means something like:

• to wipe with a cloth
• to wipe down
• to run a cloth over something

So in this sentence:

• eu passo um pano nela = I wipe it with a cloth

This is a very common everyday expression in Brazilian Portuguese.

You may also hear:

• passar um pano na mesa = wipe the table with a cloth

Nela means on it / in it, and here it refers to a mesa.

Since mesa is a feminine noun, the pronoun must also be feminine:

• mesa → feminine
• nela = em + ela

So:

• passo um pano nela = I wipe it with a cloth / I wipe on it

More literally, the structure is something like I pass a cloth on it.

If the noun were masculine, you would use:

• nele = em + ele

For example:

• no carro... passo um pano nele = on the car... I wipe it with a cloth

Yes, absolutely.

Both are natural:

• Passo um pano na mesa
• Passo um pano nela

The second version uses a pronoun to avoid repeating mesa. English does the same thing:

• There is dust on the table, so I wipe the table with a cloth
• There is dust on the table, so I wipe it with a cloth

Because um pano is the direct object of passo, and nela is a prepositional phrase referring to where the cloth is passed.

The structure is:

• passar
  • um pano
    • em/algo
• to pass
  • a cloth
    • on something

So:

• um pano = what is being used
• nela = where it is being used

That is why nela is not replacing um pano. It is replacing na mesa.

It can mean both, depending on context.

In this sentence, então is best understood as:

• so
• then

Here it connects cause and result:

• Há poeira na mesa, então eu passo um pano nela
• There is dust on the table, so I wipe it with a cloth

In everyday Portuguese, então is very common as a connector in speech.

Most naturally, it sounds like a habitual or general action:

• There is dust on the table, so I wipe it with a cloth
• meaning when that happens, that’s what I do

Portuguese present tense often covers both:

1. a present action
2. a habitual action
3. a general truth

Without more context, this sentence leans toward a habitual or routine meaning.

Yes, definitely.

That version is very natural in spoken Brazilian Portuguese:

• Tem poeira na mesa, então eu passo um pano nela

Compared with há, tem is generally:

• more conversational
• more common in speech

Compared with tem, há is generally:

• a bit more formal
• more common in writing and in textbook examples

Both are widely understood.

In this sentence, pano is a general word for cloth or rag used for cleaning.

Some related words:

• pano = cloth
• paninho = little cloth / cloth (with a softer, more affectionate or informal tone)
• flanela = flannel cloth, often specifically a dusting/polishing cloth

So passar um pano is the broad, common expression. If you change the noun, the meaning becomes a bit more specific.

The comma separates the two clauses:

• Há poeira na mesa
• então eu passo um pano nela

This is similar to English punctuation when joining two related ideas:

• There is dust on the table, so I wipe it with a cloth.

In Portuguese, using a comma before então in this kind of sentence is normal and helps readability.

Yes. The verb passar is extremely versatile in Portuguese, and its meaning depends a lot on context.

For example, passar can mean:

• to pass
• to go by
• to spend time
• to hand something over
• to apply
• to iron
• to swipe
• to wipe

But passar um pano in a sentence about dust on a table clearly means to wipe with a cloth.

Just be aware that passar is one of those verbs whose meaning changes a lot depending on the words around it.

Not naturally in most cases.

• pano is the normal word for a cleaning cloth
• toalha usually means towel
• papel means paper

If you are cleaning a table, pano is the expected choice.

You could say things like:

• papel-toalha = paper towel

But in the original sentence, um pano is the most natural everyday phrasing.