Learn Hardcore Finnish: Minä olen väsynyt, siksi juon teetä kotona.

Minä olen väsynyt – I am tired (neutral, a bit more explicit/emphatic)
Olen väsynyt – I am tired (perfectly natural, what Finns say most of the time)

You only need minä if you want to emphasize I (as opposed to someone else), e.g.:

Minä olen väsynyt, mutta sinä et ole.
I am tired, but you are not.

Is there any difference in meaning between Minä olen väsynyt and Olen väsynyt?

The basic meaning (I am tired) is the same. The difference is in emphasis:

Olen väsynyt – simple statement, neutral.
Minä olen väsynyt – stresses the subject: I am the one who is tired.
It can sound like you’re contrasting yourself with others, answering a question about who is tired, or being slightly more emotional.

In everyday conversation, Olen väsynyt is more common unless there’s a reason to emphasize minä.

What exactly does siksi mean? Is it the same as “because” or “so”?

Siksi literally means “for that reason / therefore / that’s why”. It is closer to English “so / therefore / that’s why” than to “because”.

In your sentence:

Minä olen väsynyt, siksi juon teetä kotona.
= I am tired, so I drink tea at home.
= I am tired; for that reason I drink tea at home.

You could also split it into two sentences:

Olen väsynyt. Siksi juon teetä kotona.
I am tired. That’s why I drink tea at home.

Can I use koska or joten instead of siksi in this sentence?

Yes, but the structure changes slightly.

koska = because (subordinating conjunction)
- Koska olen väsynyt, juon teetä kotona.
  Because I am tired, I drink tea at home.
- Juon teetä kotona, koska olen väsynyt.
  I drink tea at home because I am tired.
joten = so / therefore (coordinating conjunction)
- Olen väsynyt, joten juon teetä kotona.
  I am tired, so I drink tea at home.
siksi = for that reason / that’s why (adverb)
- Olen väsynyt, siksi juon teetä kotona.
  I am tired; for that reason I drink tea at home.

So:

koska introduces a reason clause (because…).
joten and siksi introduce the result (so… / therefore…), but siksi behaves more like “that’s why” than like a conjunction.

Why is there a comma before siksi?

Because the sentence has two independent clauses:

Minä olen väsynyt – I am tired
siksi juon teetä kotona – therefore I drink tea at home

In Finnish, when you join two main clauses with an adverb like siksi, you usually put a comma between them, just as in English:

Olen väsynyt, siksi menen nukkumaan.
I am tired, so I’m going to sleep.

You could also write them as two separate sentences:

Olen väsynyt. Siksi juon teetä kotona.

Why is it teetä and not just tee?

Teetä is the partitive case of tee (tea).

Finnish uses the partitive with:

an unspecified amount of something:
- juon teetä – I drink (some) tea
- ostan maitoa – I buy (some) milk
many verbs of eating/drinking, especially when the amount is not fixed.

So:

juon teen (accusative) would imply one whole, specific unit of tea (e.g. a whole cup, in some specific context) and sounds unusual on its own.
juon teetä is the natural way to say I drink tea / I am drinking tea (an indefinite amount).

Therefore the sentence uses teetä.

Why does teetä have two es?

The basic noun is tee (tea). The partitive singular ending is -ta / -tä.

Stem: tee
Add ending: tee + tä → teetä

The long vowel ee stays; Finnish does not drop one of the vowels here.

Compare:

maa → maata (land → some land)
puu → puuta (tree/wood → some wood)
kahvi → kahvia (coffee → some coffee)

So tee → teetä follows the same pattern.

Why is it kotona and not koti?

Koti means home as a basic noun. To say “at home”, you need a locative form.

Finnish has special “place forms” for koti:

kotona – at home (location)
kotiin – (to) home (movement towards)
kotoa – from home (movement away)

In your sentence, you want the static location “at home”, so you use kotona:

Juon teetä kotona. – I drink tea at home.

You would not say juon teetä koti, because koti alone doesn’t mark location.

Why not kodissa or kotissa instead of kotona?

The noun koti is a bit special. It has two sets of forms:

The very common “home” forms:
- kotona – at home
- kotiin – (to) home
- kotoa – from home
More regular case forms like kodissa, kodista, kotiin, etc., which treat koti more like a regular noun koti / kodin / kodissa (home, of a home, in a home).

Nuance:

kotona – at (my/your/etc.) home in the everyday sense: where you live, where you feel at home.
kodissa – in a home (inside a home as a physical or conceptual place). This form is much less common in simple sentences like yours and can sound more abstract or formal, e.g. lapsi kasvaa hyvässä kodissa – “a child grows up in a good home”.

For “I drink tea at home”, kotona is the natural choice.

What does juon mean exactly, and how is it related to juoda?

Juoda is the basic (dictionary) form of the verb to drink.

Juon is the 1st person singular present tense:

juon – I drink / I am drinking
juot – you drink (sing.)
juo – he/she drinks
juomme – we drink
juotte – you drink (pl.)
juovat – they drink

So in the sentence:

juon teetä kotona – I drink tea at home / I’m drinking tea at home.

You don’t need minä because the ending -n on juon already shows that the subject is “I”.

Does juon mean both “I drink” and “I am drinking”? How do I know which one?

Yes. Finnish has just one present tense form for both English “I drink” and “I am drinking”.

Juon teetä kotona.
Can mean:
- I drink tea at home (habitually), or
- I’m drinking tea at home (right now).

Context (and sometimes time words like nyt = now, aina = always) tells you which is meant:

Juon nyt teetä kotona. – I’m drinking tea at home now.
Aamuisin juon teetä kotona. – In the mornings I drink tea at home.

What kind of word is väsynyt? Is it an adjective or a verb form?

Väsynyt is grammatically a past participle of the verb väsyä (to get tired), but in everyday use it functions like an adjective meaning tired.

väsyä – to get tired, to become tired
- väsyn – I get tired
väsynyt – tired (in the state of having become tired)

So:

Olen väsynyt. – I am tired.
(literally: I am [someone who has become tired])

If you say:

Väsyn helposti. – I get tired easily.

you’re talking about the process of becoming tired, not just the state.

Can I change the word order, like Kotona juon teetä or Juon teetä siksi kotona?

Finnish word order is fairly flexible, but not all orders are equally natural.

All of these are grammatical and possible:

Juon teetä kotona. – neutral; the most common order.
Kotona juon teetä. – emphasizes at home (as opposed to somewhere else).
Teetä juon kotona. – emphasizes that tea is what I drink at home (not coffee, etc.).

But Juon teetä siksi kotona is wrong: siksi does not go between teetä and kotona like that. Siksi belongs with the second clause:

Olen väsynyt, siksi juon teetä kotona.

If you move things around, keep siksi at the beginning of the result clause:

Olen väsynyt. Siksi kotona juon teetä. – I am tired. That’s why at home I drink tea. (strong emphasis on at home)

How would I say “Because I’m tired, I drink tea at home” following English order more closely?

Use koska:

Koska olen väsynyt, juon teetä kotona.
Because I am tired, I drink tea at home.

Notes:

When the koska-clause comes first, you put a comma after it.
This order (reason first, main clause second) is very natural in Finnish.

Is it okay to say Minä olen väsynyt, siksi minä juon teetä kotona with minä twice?

It’s grammatically correct, but sounds more emphatic than usual everyday speech.

Minä olen väsynyt, siksi juon teetä kotona. – completely fine; one minä is enough.
Minä olen väsynyt, siksi minä juon teetä kotona. – stresses I in both clauses, almost like:
- I am tired, so *I drink tea at home* (maybe in contrast to someone else who does something different).

In normal neutral style, Finnish would typically drop at least one of the minä’s:

Olen väsynyt, siksi juon teetä kotona.