Learn Hardcore Finnish: Vien ostoskärryn kassan eteen ja odotan rauhassa. - I take the shopping cart in front of the checkout and wait calmly.

Vien is the 1st person singular present tense of the verb viedä (to take / to bring / to carry away).
So vien = I take / I bring (depending on context). In a shop context it often means I take/roll (something) to a place.

Why isn’t there a word for I in the sentence?

Finnish usually drops the subject pronoun because the verb ending already shows the person.
Vien already means I take/bring, so minä (I) is optional and mainly used for emphasis or contrast.

Why is it ostoskärryn with -n at the end?

Ostoskärryn is the object in the so-called total object form. For many singular total objects, Finnish uses a form that looks like the genitive (ending -n).
Base form: ostoskärry (shopping cart)
Object here: ostoskärry + n → ostoskärryn (the cart, as a complete/definite action: you take the cart to a specific place).

What’s the difference between ostoskärryn and ostoskärryä?

It’s largely about whether the action is seen as complete/whole or partial/ongoing.

Vien ostoskärryn... = I take the cart (as a whole; the action has a clear endpoint).
Vien ostoskärryä... = I’m taking a cart / some of the cart, or the action is in progress / not bounded (often sounds odd with a cart unless you’re emphasizing the process or an unfinished action).

With ...kassan eteen (a clear destination), ostoskärryn is the natural choice.

What does kassan eteen mean grammatically? Why two words?

It’s a common Finnish structure: [noun in genitive] + postposition.

kassan = genitive of kassa (checkout/cash register/checkout area)
eteen = postposition meaning to (the) front of (direction/motion)

So kassan eteen literally = to the front of the checkout.

Why is it eteen (to the front) and not edessä (in front)?

Because the sentence describes movement toward a position.

kassan eteen = to in front of the checkout (motion → destination)
kassan edessä = in front of the checkout (static location)

Here you move the cart to that spot, so eteen fits.

What exactly does kassa refer to here: the cashier, the register, or the checkout?

In everyday Finnish, kassa commonly refers to the checkout as a place/service point (including the register area), and sometimes by extension the cashier station.
So kassan eteen is naturally understood as in front of the checkout line / register area.

Why is it kassan (with double s)?

That’s just how the genitive is formed for this word:

Base form: kassa
Genitive: kassan

Finnish often doubles consonants in certain word patterns when adding endings; here it’s simply the standard inflection for kassa.

What case is rauhassa, and why is it used to mean “calmly”?

Rauhassa is the inessive case of rauha (peace, calm):

rauha = calm/peace
rauhassa = in (a state of) calm/peace

Finnish often uses location/state cases adverbially, so odotan rauhassa means I wait calmly / I wait in peace.

Could you say odotan rauhallisesti instead of odotan rauhassa?

Yes, both are possible.

odotan rauhassa = very common, idiomatic; emphasizes being in a calm state
odotan rauhallisesti = also correct; more directly “calmly” as an adverb

They’re close in meaning; rauhassa often feels a bit more natural and conversational.

Is the word order fixed? Could parts be moved around?

Finnish word order is fairly flexible, but changes often add emphasis.

Neutral/natural here: Vien ostoskärryn kassan eteen ja odotan rauhassa.

Possible variations:

Vien kassan eteen ostoskärryn... = emphasizes the destination (to the checkout front)
Ja odotan rauhassa could be moved earlier for contrast, but the given order is the most straightforward narrative sequence: do action 1, then action 2.