La firmao havas grandan potencon.

Because they are the direct object of the verb havas.

In Esperanto, the thing directly affected by the verb usually takes -n. Here, the company has something: great power. So potenco becomes potencon.

The adjective has to agree with the noun, so granda also takes the same ending and becomes grandan.

So:

• potenco = power
• potencon = power, as a direct object
• granda potenco = great power
• grandan potencon = great power, as a direct object

Because after havas, the noun phrase is the object, not the subject.

Compare:

• Granda potenco estas danĝera. = Great power is dangerous.
  Here granda potenco is the subject, so there is no -n.
• La firmao havas grandan potencon. = The company has great power.
  Here grandan potencon is the object, so it takes -n.

So the ending is showing grammatical function, not just meaning.

In Esperanto, adjectives must agree with the nouns they describe in:

• number: singular or plural
• case: whether they have the accusative -n

Since potencon is singular and accusative, the adjective must match it:

• granda potenco
• grandan potencon
• grandaj potencoj
• grandajn potencojn

This agreement is very regular in Esperanto.

La is the definite article, meaning the.

So la firmao means the company.

Esperanto has only one article:

• la = the

It does not have a separate word for a or an. So:

• firmao = a company / company
• la firmao = the company

It is used here because the speaker is talking about a specific company, not just any company in general.

Because Esperanto has no indefinite article.

English distinguishes between:

• the company
• a company

But Esperanto only marks the definite article:

• la firmao = the company
• firmao = a company / company

So grandan potencon can naturally mean great power without any extra word for a.

Havas is the present-tense form of the verb havi, meaning to have.

Esperanto verb endings are very regular:

• havi = to have
• havas = has / have
• havis = had
• havos = will have
• havu = have! / let ... have
• havant- forms also exist, but those are participial

The ending -as always marks the present tense, regardless of the subject:

• mi havas = I have
• vi havas = you have
• la firmao havas = the company has

It is a normal Esperanto word, but like many Esperanto words, it comes from an international root.

Firmao means company, firm, business enterprise. It is built in a very Esperanto-like way:

• root: firm-
• noun ending: -o

So firmao is a noun.

Even when a root is internationally familiar, Esperanto still gives it regular grammar and word-building.

Yes, in many contexts povo and potenco are related, but they are not always exactly the same.

A common distinction is:

• povo = ability, capacity, possibility to do something
• potenco = power, force, influence, authority, strength

So:

• havas grandan povon can suggest has great ability/capacity
• havas grandan potencon often suggests has great power/influence

In many real-life sentences there can be overlap, but potenco is a very natural choice for power in the sense of influence or strength.

Usually, the normal and most natural order is:

• grandan potencon

Esperanto does allow flexible word order, so potencon grandan is grammatically possible, but it sounds marked or poetic in ordinary usage.

For a learner, the safest pattern is:

• article
• noun phrase with adjective before noun
• verb/object as needed

So in normal prose and speech, grandan potencon is the best choice.

Esperanto pronunciation is very regular.

• firmao = fir-MA-o
• potencon = po-TEN-tson

A few useful points:

• Stress is always on the second-to-last syllable.
• c is pronounced ts.
• Each vowel is pronounced clearly.

So:

• La firMAo HAvas granDAN poTENtson.

Yes, to some extent.

Because grandan potencon has the accusative -n, Esperanto can show that it is the object even if the order changes. For example:

• La firmao havas grandan potencon.
• Grandan potencon la firmao havas.

Both are grammatical.

However, the first version is the most neutral and natural. The second puts extra emphasis on grandan potencon.

So the -n gives flexibility, but neutral word order is still most common.

No. Potenco can refer to power in several senses, depending on context, such as:

• influence
• authority
• force
• strength
• power in a general abstract sense

In this sentence, with company, many learners will understand it as something like:

• influence
• economic power
• corporate power

So it is broader than only political power.