Learn Hardcore Finnish: Nämä ystävät, jotka opiskelevat suomea, ovat täällä nyt. - These friends, who study Finnish, are here now.

Nämä means these (near the speaker) and is the nominative plural form of the demonstrative pronoun tämä. It directly modifies ystävät: nämä ystävät = these friends.

Ne can mean they or those. In many spoken contexts ne is used for both they and those, but in standard written Finnish:

nämä ystävät = these friends (near, more specific)
ne ystävät = those friends (usually more distant or already known in the context)

In your sentence, nämä emphasizes these particular friends (here/near us).

Why is there a comma before and after jotka opiskelevat suomea?

Jotka opiskelevat suomea is a relative clause (who are studying Finnish) describing ystävät.

In Finnish, a non‑restrictive relative clause (extra information, not needed to identify which friends) is usually separated by commas, just like in English:

Nämä ystävät, jotka opiskelevat suomea, ovat täällä nyt.
= These friends, who are studying Finnish, are here now.

If you drop the commas in Finnish, it tends to sound more like a restrictive clause (only the friends who study Finnish, as opposed to some other friends). In practice, Finnish punctuation is a bit looser than English, but the commas here show that the clause is additional information about nämä ystävät.

What exactly does jotka mean, and why is it jotka and not joka?

Joka is a relative pronoun similar to who / which / that in English.

It agrees in number and case with the word it refers to:

Singular nominative: joka (who/which/that)
Plural nominative: jotka (who/which/that – plural)

Here, jotka refers to ystävät (friends), which is plural, so you must use jotka:

ystävä, joka opiskelee suomea = a friend who studies Finnish
ystävät, jotka opiskelevat suomea = friends who study Finnish

So jotka = who (referring to a plural noun).

Why is opiskelevat in that form? What person/number is it?

Opiskelevat is the 3rd person plural form of the verb opiskella (to study):

hän opiskelee = he/she studies, is studying
he opiskelevat = they study, are studying

In the relative clause jotka opiskelevat suomea, the subject is jotka referring back to ystävät (plural). So the verb also has to be plural:

ystävä, joka opiskelee suomea (singular)
ystävät, jotka opiskelevat suomea (plural)

That is why we use opiskelevat, not opiskelee.

Why is it suomea and not suomi after opiskelevat?

Suomi is the nominative form (dictionary form) of Finnish.
Suomea is the partitive form.

Many verbs that express studying, learning, teaching, knowing a language, etc. typically take the partitive when the object is a language:

opiskella suomea = to study Finnish
opiskella englantia = to study English
opetella ruotsia = to learn Swedish

So jotka opiskelevat suomea is the natural, idiomatic way to say who are studying Finnish. Using suomi in nominative (opiskelevat suomi) would be incorrect here.

Why is the verb ovat (are) plural and not on (is)?

In Finnish, the verb usually agrees with the number of the subject.

ystävä on täällä = the friend is here
ystävät ovat täällä = the friends are here

The subject in your sentence is nämä ystävät (these friends), which is plural. Therefore, the correct form of olla (to be) is ovat:

Nämä ystävät … ovat täällä nyt.
= These friends … are here now.

Could I say Nämä ystävät ovat nyt täällä instead of …ovat täällä nyt? Does the word order change the meaning?

Yes, you can say both:

Nämä ystävät, jotka opiskelevat suomea, ovat täällä nyt.
Nämä ystävät, jotka opiskelevat suomea, ovat nyt täällä.

Both are grammatically correct and basically mean the same thing: These friends … are here now.

Subtle difference:

…ovat täällä nyt puts a neutral focus on the location first, then adds now.
…ovat nyt täällä can slightly highlight the time change (they are now here, maybe they weren’t before).

In everyday speech, both orders are very common; context and intonation carry most of the nuance.

Can I move the relative clause to the end, like Nämä ystävät ovat täällä nyt, jotka opiskelevat suomea?

No, that word order is not natural in Finnish. The relative clause normally comes immediately after the noun it describes:

✅ Nämä ystävät, jotka opiskelevat suomea, ovat täällä nyt.
❌ Nämä ystävät ovat täällä nyt, jotka opiskelevat suomea.

If you want the information at the end, you would typically rephrase the sentence, for example with ja:

Nämä ystävät ovat täällä nyt ja opiskelevat suomea.
= These friends are here now and (they) study / are studying Finnish.

Does jotka opiskelevat suomea mean “who study Finnish” or “who are studying Finnish”? How does tense/aspect work here?

Finnish doesn’t have a separate continuous tense like English (no direct equivalent of are studying). The present tense opiskelevat can cover both:

who study Finnish (habitual, general)
who are studying Finnish (right now / currently, as an ongoing activity)

The exact nuance comes from context, not from a different verb form. So jotka opiskelevat suomea can be translated either way depending on what fits the situation best.

Could I leave out nämä and just say Ystävät, jotka opiskelevat suomea, ovat täällä nyt?

Yes, that is grammatically correct. It would mean The friends who are studying Finnish are here now, or simply The friends … are here now, depending on context.

Nämä ystävät = these friends (more pointed, like you are indicating or contrasting them)
Ystävät = the friends (assumes the listener already knows which friends you mean)

Using nämä adds a demonstrative meaning: you are specifically pointing out these friends (as opposed to some other group).

How would I say Those friends who are studying Finnish are here now?

You can use ne (those) instead of nämä:

Ne ystävät, jotka opiskelevat suomea, ovat täällä nyt.

This highlights that the friends are not close to the speaker (physically or contextually), or that you’re contrasting them with some other friends. The rest of the structure stays the same.

Is there any word for “who” or “that” missing in the English translation, or does jotka fully cover it?

Jotka fully covers what English expresses with who / which / that in this context. It is a gender‑neutral relative pronoun:

for people: ystävät, jotka… = friends who…
for things: kirjat, jotka… = books that / which…

So in this sentence, jotka corresponds to who in English:
Nämä ystävät, jotka opiskelevat suomea, ovat täällä nyt.
= These friends, who are studying Finnish, are here now.