Mi ne volas porti pezan sakon en la urbo.

Mi is the Esperanto subject pronoun meaning I.

Esperanto pronouns do not change form the way English pronouns do. So:

• mi = I
• min = me

In this sentence, mi is the subject, the person doing the action, so mi is correct.

In Esperanto, ne normally goes directly before the word it negates.

Here, ne negates volas, so the sentence means:

• Mi ne volas... = I do not want...

This is the normal and most natural placement.

Compare:

• Mi ne volas porti... = I do not want to carry...
• Mi volas ne porti... = I want not to carry... / I want to avoid carrying...

The second version is possible, but it has a more specific emphasis. The original sentence is the usual way to say it.

Volas is the present-tense form of voli, meaning to want.

Esperanto verbs always have predictable endings:

• -i = infinitive, as in voli = to want
• -as = present tense, so volas = want / am wanting

So:

• mi volas = I want

There is no separate form for do as in English I do not want. Esperanto simply uses ne with the verb:

• Mi ne volas = I do not want

Because porti is an infinitive: to carry or to wear, depending on context.

After verbs like voli (to want), Esperanto usually uses an infinitive:

• Mi volas porti = I want to carry

This works very much like English want to carry.

Other examples:

• Mi volas iri = I want to go
• Ŝi volas manĝi = She wants to eat

Because pezan describes sakon, and sakon is the direct object of porti.

In Esperanto, the direct object usually takes -n. Since adjectives must agree with the nouns they describe, peza also becomes pezan.

So:

• peza sako = a heavy bag
• pezan sakon = a heavy bag, as a direct object

Both words take -n because they go together:

• pezan matches sakon

This agreement is one of the most important patterns in Esperanto.

Sakon has the accusative ending -n, which marks the direct object.

Ask: what is being carried?

Answer: pezan sakon

So sakon is the thing affected by the action porti, and that is why it gets -n.

Compare:

• La sako estas peza. = The bag is heavy.
  
  • Here sako is the subject, so no -n.
• Mi portas la sakon. = I am carrying the bag.
  
  • Here sakon is the direct object, so it takes -n.

They do not have the same ending exactly, but they both show two pieces of grammar:

• peza = adjective ending -a
• sako = noun ending -o

Then both add -n because they are in the accusative:

• peza → pezan
• sako → sakon

So the endings break down like this:

• pez-a-n = heavy + adjective + accusative
• sak-o-n = bag + noun + accusative

This is adjective-noun agreement in Esperanto:

• same number
• same case

La is the definite article, meaning the.

So:

• en la urbo = in the city

Without la, en urbo would mean something more like in a city or in city settings, but that is less normal here unless the speaker wants to be deliberately less specific.

Esperanto has only one article:

• la = the

There is no separate word for a or an. Often Esperanto simply leaves it unexpressed.

So:

• sako = a bag / bag
• la sako = the bag

Because here en shows location, not motion into something.

• en la urbo = in the city
• en la urbon = into the city

The -n after a preposition is often used when there is movement toward a place.

Compare:

• Mi estas en la urbo. = I am in the city.
• Mi iras en la urbon. = I am going into the city.

In your sentence, the idea is carrying the bag while being in the city, so simple location is meant, and urbo does not take -n.

It can mean both, depending on context.

Common uses:

• porti sakon = carry a bag
• porti ĉapelon = wear a hat

In this sentence, because the object is pezan sakon, the natural meaning is carry.

So context tells you which English verb is best.

Yes, Esperanto word order is fairly flexible, but some orders are more neutral than others.

The original sentence:

• Mi ne volas porti pezan sakon en la urbo.

is the most straightforward, neutral order.

Because sakon has -n, Esperanto can move parts around more freely without losing the basic meaning. For example:

• En la urbo mi ne volas porti pezan sakon.
• Pezan sakon mi ne volas porti en la urbo.

These versions may change emphasis, but the grammar still works.

Even so, learners should usually prefer the most neutral order first.

In the most natural reading, en la urbo tells you where the action happens:

• I don’t want to carry a heavy bag in the city.

That is because prepositional phrases like en la urbo often describe the setting of the action.

Could it theoretically describe the bag? In some contexts, people might momentarily wonder, but here common sense strongly points to the action:

• the carrying happens in the city

If you wanted to be extra clear, context or rephrasing would help, but the original sentence is perfectly normal.

Because Esperanto infinitives do not need a separate word like English to.

The infinitive is shown by the ending -i:

• porti = to carry
• voli = to want
• iri = to go

So Mi volas porti already means I want to carry.

The meaning of English to is built into the infinitive ending.

It is built in a very regular Esperanto way:

• pez- = weight / heaviness-related root
• -a = adjective ending

So peza means heavy.

Then:

• pez-a-n = heavy, accusative form

This regular structure is very typical of Esperanto and helps learners recognize word families, such as:

• pezo = weight
• peza = heavy
• peze = heavily

A useful breakdown is:

• Mi = subject
• ne volas = negated main verb
• porti = infinitive complement
• pezan sakon = direct object of porti
• en la urbo = prepositional phrase showing location

So the structure is roughly:

subject + negation + main verb + infinitive + object + place

That pattern is very common in Esperanto.