Mi havas nigran jakon.

Because jakon is the direct object of the verb havas.

In Esperanto, the direct object usually takes -n.
Here:

• Mi = subject
• havas = verb
• jakon = thing being had, so it gets -n

Base form: jako
In the sentence: jakon

Because adjectives in Esperanto agree with the noun they describe.

Since jakon has -n, the adjective describing it must also have -n:

• nigra jako = a black jacket
• nigran jakon = a black jacket as a direct object

So both words match:

• nigran = adjective + object ending
• jakon = noun + object ending

Esperanto does not have an indefinite article like English a/an.

So:

• jako can mean a jacket
• la jako means the jacket

That is why Mi havas nigran jakon naturally means I have a black jacket without needing a separate word for a.

The dictionary forms are:

• mi = I
• havi = to have
• nigra = black
• jako = jacket

In the sentence, some forms change:

• havi → havas because it is present tense
• nigra → nigran because it agrees with the direct object
• jako → jakon because it is the direct object

Because -as is the Esperanto ending for the present tense.

So:

• havas = have / has

Esperanto verbs do not change according to the subject the way English verbs do. So you get:

• mi havas = I have
• vi havas = you have
• li havas = he has
• ili havas = they have

The verb form stays havas for all of them.

The most normal word order is:

• subject + verb + object

So Mi havas nigran jakon is the standard, natural order.

Because Esperanto marks the direct object with -n, word order can sometimes be changed more freely than in English. But for a learner, the safest and most natural version is the one here.

Yes, it is grammatically possible, because Esperanto allows some flexibility in adjective placement.

But it is less neutral and less common than nigran jakon. For ordinary speech and writing, learners should usually put the adjective before the noun:

• nigran jakon = the normal phrasing

So Mi havas nigran jakon is the best choice here.

No. That is incorrect.

The adjective must agree with the noun. Since jakon has -n, the adjective must also have -n:

• correct: nigran jakon
• incorrect: nigra jakon

Agreement is an important rule in Esperanto.

A simple pronunciation guide is:

• Mi ≈ mee
• havas ≈ HAH-vahs
• nigran ≈ NEE-grahn
• jakon ≈ YAH-kon

A few useful pronunciation points:

• j sounds like English y
• stress usually falls on the second-to-last syllable
• each letter is pronounced clearly

So the stress is:

• HA-vas
• NI-gran
• JA-kon

Not necessarily.

Mi havas nigran jakon means that you have / own / possess a black jacket.

If you want to say that you are wearing it, you would normally use porti:

• Mi portas nigran jakon = I am wearing a black jacket

So havas is about possession, not specifically wearing.

You add -j for plural, and if it is still the direct object, you also keep -n.

So:

• singular: Mi havas nigran jakon = I have a black jacket
• plural: Mi havas nigrajn jakojn = I have black jackets

Notice that both the adjective and the noun change:

• nigra → nigraj → nigrajn
• jako → jakoj → jakojn

This shows both plural and direct object.