Mia kara amiko venis.

Because -is is the Esperanto ending for the past tense.

• veni = to come
• venis = came / has come

So Mia kara amiko venis means that the coming happened in the past.

Yes. The dictionary form is veni (to come). Esperanto verbs change their endings regularly:

• veni = to come
• venas = comes / is coming
• venis = came
• venos = will come
• venus = would come
• venu = come! / let ... come

So in this sentence, veni becomes venis.

Because mi means I, while mia means my.

• mi = I
• mia = my

In Esperanto, possessive words are formed very regularly:

• mi → mia = my
• vi → via = your
• li → lia = his
• ŝi → ŝia = her

So mia amiko means my friend.

Because adjectives in Esperanto normally end in -a.

• kara = dear
• bona = good
• granda = big

So kara amiko means dear friend.

Because both function like adjectives here and describe amiko.

• mia = my
• kara = dear
• amiko = friend

In Esperanto, adjectives agree with the noun they describe. Since amiko is singular and has no accusative -n, the describing words stay in the basic -a form:

• mia kara amiko = my dear friend

If the noun were plural, they would change too:

• miaj karaj amikoj = my dear friends

Because this sentence has a subject, not a direct object.

• amiko is the one doing the action: the friend came.
• Since it is the subject, it stays in the basic form: amiko

The -n ending is mainly used for a direct object:

• Mi vidis mian amikon. = I saw my friend.

But with venis, there is no direct object here. Veni is an intransitive verb, so it normally does not take one.

Yes, Esperanto allows fairly flexible word order, and adjectives can come after the noun. But kara amiko is the more normal and natural order here.

• kara amiko = the usual way
• amiko kara = possible, but more marked or poetic

For a beginner, it is safest to put adjectives before the noun unless you have a reason not to.

Because Esperanto does not use la when a possessive already makes the noun definite.

• mia amiko = my friend
• not usually la mia amiko

Just like in English, you normally say my friend, not the my friend.

So mia already does the job of making it specific.

Not necessarily. In modern Esperanto, amiko is usually understood as friend without needing to specify gender.

If you want to make gender explicit, Esperanto has forms such as:

• amiko = friend
• amikino = female friend

In many contexts, amiko can be used in a general sense.

No, not in this sentence. Kara often means dear in the emotional sense, as in dear friend.

Depending on context, kara can also mean costly or expensive, but here with amiko, the natural meaning is clearly dear or beloved.

So mia kara amiko means my dear friend, not my expensive friend.

Yes. Esperanto past tense does not work exactly like English tense systems. -is simply marks the action as past.

So venis may be translated as:

• came
• has come

The best English translation depends on context.

The subject is amiko.

More exactly, the full subject phrase is:

• mia kara amiko = my dear friend

That whole phrase is the person who did the action, and the action is venis.

So the structure is:

• Mia kara amiko = subject
• venis = verb

A simple pronunciation guide is:

MEE-ah KAH-rah ah-MEE-koh VEH-nees

A few helpful points:

• mi sounds like mee
• a is like ah
• k is always hard, like in skin
• v is like English v
• stress is normally on the second-to-last syllable

So:

• Mia → MI-a
• kara → KA-ra
• amiko → a-MI-ko
• venis → VE-nis

Yes. That is grammatically correct too.

Esperanto word order is flexible because endings show grammatical roles clearly. So both of these work:

• Mia kara amiko venis.
• Venis mia kara amiko.

The first is the most straightforward and neutral for learners. The second may sound a little more stylistic or emphasize the action first.