Learn Hardcore Finnish: Ystäväni on kärsivällinen, kun minä opiskelen suomea. - My friend is patient when I study Finnish.

minun is the genitive form of minä (I), so minun = my.
In standard written Finnish, using both minun and the suffix -ni (minun ystäväni) is considered normal and slightly more emphatic: my friend (not someone else’s).
Ystäväni alone is completely correct and often enough.
In colloquial spoken Finnish, people often say mun ystävä (mun = spoken form of minun) without the suffix: Mun ystävä on kärsivällinen.

So:

Standard: Ystäväni / Minun ystäväni
Colloquial: Mun ystävä

Do I have to include minä in kun minä opiskelen suomea, or can I drop it?

You can drop it. Both are correct:

kun minä opiskelen suomea
kun opiskelen suomea

Finnish verb endings already show the person:

opiskelen = I study

So minä is not grammatically required. Adding minä gives emphasis or contrast, like:

Kun minä opiskelen suomea, ystäväni tekee ruokaa.
= When I am studying Finnish (as opposed to someone else), my friend cooks.

Why is opiskelen used instead of the dictionary form opiskella?

Opiskella is the infinitive form: to study.
In a sentence, you usually need a conjugated verb form.

Present tense of opiskella (to study):

minä opiskelen = I study / I am studying
sinä opiskelet = you study
hän opiskelee = he/she studies
me opiskelemme = we study
te opiskelette = you (pl) study
he opiskelevat = they study

So in minä opiskelen suomea, opiskelen is 1st person singular present tense: I study.

What does kun mean here, and how is it different from jos?

In this sentence, kun means when or whenever:

Ystäväni on kärsivällinen, kun minä opiskelen suomea.
= My friend is patient when I study Finnish.

Contrast with jos:

kun = when, for real or repeated situations:
- Kun tulen kotiin, syön. = When I come home, I eat.
jos = if, for conditions or possibilities:
- Jos tulen kotiin, syön. = If I come home, I’ll eat.

So you use kun here because it’s about something that actually happens when you study, not a hypothetical if.

Why is there a comma before kun in Finnish?

In standard Finnish punctuation, you put a comma between the main clause and a subordinate clause introduced by words like kun, että, koska, jos, vaikka, etc., no matter the order.

So you write:

Ystäväni on kärsivällinen, kun minä opiskelen suomea.
Kun minä opiskelen suomea, ystäväni on kärsivällinen.

Both must have a comma between the clauses. This is stricter than in English, where the comma can sometimes be omitted.

Why is suomea used here instead of suomi?

Suomea is the partitive form of suomi (Finnish language):

suomi = Finnish (language), nominative
suomea = Finnish, partitive singular

In Finnish, the partitive case is often used:

for ongoing / incomplete actions
for indefinite amounts or “not-whole” objects

Verbs like opiskella (to study), puhua (to speak), ymmärtää (to understand) commonly take languages in the partitive:

opiskella suomea = study Finnish
puhua suomea = speak Finnish
ymmärtää suomea = understand Finnish

You would not say opiskelen suomi; that sounds wrong.
So opiskelen suomea is the natural, correct form.

Why is suomea not capitalized, even though Finnish is capitalized in English?

In Finnish:

names of languages and nationalities are not capitalized:
- suomi / suomea = Finnish (language)
- englanti / englantia = English (language)
- suomalainen = Finnish (person, adjective)
names of countries and other proper names are capitalized:
- Suomi = Finland
- Iso-Britannia = Great Britain

So opiskelen suomea is correct with a lowercase s.

Can I change the word order to Kun minä opiskelen suomea, ystäväni on kärsivällinen?

Yes. Both are correct:

Ystäväni on kärsivällinen, kun minä opiskelen suomea.
Kun minä opiskelen suomea, ystäväni on kärsivällinen.

The meaning is the same: My friend is patient when I study Finnish.

The difference is mostly in emphasis / information flow:

Starting with Ystäväni on kärsivällinen... focuses first on your friend.
Starting with Kun minä opiskelen suomea... focuses first on the time/situation.

But grammatically, both are fine.

Can I leave out on and just say Ystäväni kärsivällinen?

In standard Finnish, you need the verb olla (“to be”):

Ystäväni on kärsivällinen. = My friend is patient.

Just Ystäväni kärsivällinen is not correct in normal written Finnish.

In very casual spoken language, people sometimes drop on in some contexts:

Mun ystävä tosi kärsivällinen.

But this is colloquial speech, not something you should write in standard Finnish. For correct, neutral Finnish, always include on.

How would I say My friends are patient when I study Finnish?

One natural way:

Ystäväni ovat kärsivällisiä, kun opiskelen suomea.

Breakdown:

ystäväni = my friend / my friends
- This form is ambiguous (it can be singular or plural);
  ovat (are) shows that it’s plural here: my friends.
ovat = are (3rd person plural of olla)
kärsivällisiä = patient (partitive plural of kärsivällinen)
kun opiskelen suomea = when I study Finnish (here you can drop minä)

So:

Ystäväni ovat kärsivällisiä, kun opiskelen suomea.
= My friends are patient when I study Finnish.

How can I tell if ystäväni is male or female? Does Finnish have gender?

From ystäväni alone, you cannot tell whether the friend is male or female. Finnish:

does not have grammatical gender for nouns
uses one pronoun, hän, for both he and she

So:

ystäväni = my friend (no gender information)
Hän on kärsivällinen. = He/She is patient.

If you need to specify, you add extra words like miespuolinen ystäväni (my male friend) or naispuolinen ystäväni (my female friend), or just explain in context.