Minä sotken keittiötä, kun teen ruokaa.

That is true: Finnish often leaves out the subject pronoun when the verb form already shows the person.

So this sentence could also be:

Sotken keittiötä, kun teen ruokaa.

Including minä can add:

• emphasis
• contrast
• a slightly more explicit tone

So minä is not required here, but it is not wrong at all.

Sotken is the 1st person singular present tense of sotkea.

• sotkea = to mess up, make messy, mix up
• sotken = I mess up / I make a mess / I am messing up

In this sentence it means I make a mess of the kitchen.

Because Finnish often uses the partitive object when an action is seen as:

• ongoing
• not completed
• not result-focused

Here, sotken keittiötä suggests the process of making the kitchen messy, especially while cooking.

Compare:

• sotken keittiötä = I am making a mess of the kitchen / I tend to mess up the kitchen
• sotken keittiön = I mess up the kitchen completely; the result is emphasized more strongly

So the partitive fits well because the sentence describes an activity happening during another activity.

For a very similar reason.

Teen ruokaa is a common Finnish expression meaning I cook or I make food. The partitive ruokaa presents it as an ongoing activity rather than a completed product.

Compare:

• teen ruokaa = I am cooking / making food
• teen ruoan = I make the meal, with the meal seen as a completed whole

So teen ruokaa sounds very natural here.

Here kun means when or whenever.

It introduces a subordinate clause:

• kun teen ruokaa = when I cook / when I am cooking

In some other contexts, kun can also mean something like since or because, but in this sentence the meaning is clearly temporal.

It can mean either, depending on context.

Finnish present tense is flexible. This sentence can mean:

• right now: I am making a mess of the kitchen while I cook
• habitually: I make a mess of the kitchen whenever I cook

Because of kun teen ruokaa, many learners will first read it as a general/habitual statement: whenever I cook, I make a mess.

Because Finnish usually does not have a separate future tense.

The present tense is used for:

• present actions
• habitual actions
• future actions, if the context makes the time clear

So Finnish does not need a special future form here.

Yes, absolutely.

That version is also natural:

Kun teen ruokaa, sotken keittiötä.

Finnish word order is more flexible than English word order. Both versions are grammatical.

The difference is mainly about focus:

• Minä sotken keittiötä, kun teen ruokaa. → starts with the main point
• Kun teen ruokaa, sotken keittiötä. → starts with the time clause

Because in this sentence the kitchen is the object of the verb sotkea.

You are not just doing something in the kitchen. You are making the kitchen itself messy.

• keittiötä = the kitchen, as the thing being messed up
• keittiössä = in the kitchen, as a location

So:

• Sotken keittiötä = I mess up the kitchen
• Sotken keittiössä = I make a mess in the kitchen / I mess around in the kitchen

Those are not exactly the same idea.

Yes, you could, but the meaning shifts a bit.

• sotken keittiötä = I am making a mess of the kitchen; the action is ongoing or unbounded
• sotken keittiön = I mess up the kitchen; the result is more strongly emphasized

In this sentence, with kun teen ruokaa, the partitive keittiötä sounds very natural because it matches the idea of an ongoing activity while cooking.

Because tehdä ruokaa is a very common and natural way to say to cook or to make food.

Other options are possible too:

• teen ruokaa = I make food / cook
• laitan ruokaa = I prepare food / cook
• kokkaan = I cook

All can work, but teen ruokaa is simple, common, and neutral.