Minä sotken pöytää, kun syön aamupalaa.

Yes. In normal Finnish, minä is often omitted because the verb ending already shows the subject.

• sotken = I mess up / I make messy
• syön = I eat

So Sotken pöytää, kun syön aamupalaa is a very natural version.

Including minä adds a little emphasis, contrast, or clarity. It can sound like I (as opposed to someone else) make a mess.

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

• infinitive: sotkea = to mess up, make messy, mix up
• present 1st person singular: sotken = I mess up / I make messy

So the sentence uses the present tense. In English, that can correspond to either:

• I make a mess
• I am making a mess

depending on context.

Pöytää is the partitive singular of pöytä.

Here it is the object of sotken, and Finnish often uses the partitive object when the action is:

• ongoing
• incomplete
• repeated/habitual
• not presented as reaching a clear endpoint

So sotken pöytää suggests something like I am messing up the table / making the table messy, with the action seen as in progress or unbounded.

Compare:

• Sotken pöytää = I’m making the table messy / messing up the table
• Sotkin pöydän = I messed up the table (completed result)

Because syödä very often takes the partitive when you are eating:

• an unspecified amount
• something uncountable in context
• a meal as an activity rather than a complete object

So:

• syön aamupalaa = I eat breakfast / I’m eating breakfast

This is very normal Finnish.

Compare that with a clearly complete object:

• Syön omenan = I eat the apple / I will eat the whole apple

Meal words often behave like this:

• syön aamupalaa
• syön lounasta
• syön päivällistä

Here kun means when.

In this sentence it introduces a time clause:

• kun syön aamupalaa = when I eat breakfast / while I’m eating breakfast

Depending on the English wording, it can feel like:

• when
• while
• as

In other sentences, kun can also mean because, but that is not the meaning here.

For the same reason as in the main clause: the verb ending already tells you the subject.

• syön = I eat

So kun syön aamupalaa already means when I eat breakfast.

You could say kun minä syön aamupalaa, but that would sound more emphatic, like when I eat breakfast.

It can mean either, depending on context.

Finnish present tense often covers both:

• habitual meaning: I make a mess when I eat breakfast
• ongoing/current meaning: I’m making a mess of the table while I’m eating breakfast

English often has to choose between simple present and present progressive, but Finnish usually just uses the present tense.

Yes. You can also say:

Kun syön aamupalaa, sotken pöytää.

That means the same thing overall.

The difference is mainly about emphasis and information flow:

• Minä sotken pöytää, kun syön aamupalaa.
  starts with the main point: I make a mess
• Kun syön aamupalaa, sotken pöytää.
  starts with the time/background: when I eat breakfast

Both are grammatical.

Because kun syön aamupalaa is a subordinate clause.

In Finnish, a subordinate clause is normally separated from the main clause with a comma:

• Minä sotken pöytää, kun syön aamupalaa.
• Kun syön aamupalaa, sotken pöytää.

This is standard Finnish punctuation.

Both are partitive singular forms.

• pöytä → pöytää
• aamupala → aamupalaa

A simple way to think of it is that many nouns ending in -a / -ä form the partitive singular with an extra -a / -ä, which gives:

• -aa
• -ää

So:

• aamupala → aamupalaa
• pöytä → pöytää

This is a very common pattern, and you will see it a lot in basic Finnish.

Because Finnish treats the table as the thing being affected by sotkea.

So sotkea pöytää literally works like to mess up the table / make the table messy.

Even if an English translation might sometimes sound more natural as make a mess at the table or make a mess on the table, Finnish expresses it with the table as the object of the verb.

So the structure is normal Finnish, even if English might phrase the idea a little differently.