Когда я готовлю, я надеваю фартук, чтобы соус не попал на рубашку.

Готовлю is the imperfective verb, and here it means when/whenever I cook in a general, repeated sense.

• Когда я готовлю... = When/Whenever I cook...
• It describes a habitual situation, not one specific completed cooking event.

A form like приготовлю would mean I will prepare/cook (and finish), which does not fit this general statement.

So the sentence is talking about a routine:

• When I cook, I wear an apron...

That is very common in Russian. Когда can mean:

• when in a specific situation
• whenever in a repeated or habitual situation

In this sentence, because готовлю suggests a repeated activity, Когда я готовлю naturally means:

• When I cook
• or more explicitly, Whenever I cook

Russian often uses когда where English might prefer whenever.

Russian often repeats the subject even when English might leave it out.

So:

• Когда я готовлю, я надеваю фартук
  literally: When I cook, I put on an apron

The second я is not required in every situation, but it is very normal and natural. It helps make the second clause clear and complete.

You could sometimes omit it in conversation, but this full version is standard and easy to understand.

Because Когда я готовлю is a subordinate clause.

Russian uses commas very consistently to separate subordinate clauses from the main clause:

• Когда я готовлю, я надеваю фартук...

This is true even where English might be less strict in some contexts. In Russian, with когда, чтобы, если, and similar conjunctions, a comma is usually expected.

This is a classic learner question.

In standard Russian:

• надевать / надеть = to put on an item of clothing
• одевать / одеть = to dress a person

So:

• Я надеваю фартук = I put on an apron
• Я одеваю ребёнка = I dress the child

A useful shortcut:

• You надеть something
• You одеть someone

Native speakers do sometimes blur this in casual speech, but for learners, надеваю фартук is the correct choice.

Фартук is in the accusative case, because it is the direct object of надеваю.

However, for many masculine inanimate nouns, the accusative singular looks exactly like the nominative singular.

So:

• Nominative: фартук
• Accusative: фартук

That is why you do not see a different ending here.

Чтобы often means so that, in order that, or so as to.

In this sentence:

• Я надеваю фартук, чтобы соус не попал на рубашку.
• I put on an apron so that the sauce doesn’t get on my shirt.

It introduces the purpose of wearing the apron.

So the structure is:

• main action: I put on an apron
• purpose: so that the sauce won’t get on my shirt

After чтобы, Russian often uses a form that looks like the past tense, but in this structure it does not simply mean past time.

Here:

• чтобы соус не попал = so that the sauce won’t get / doesn’t get

This is a very normal Russian pattern:

• чтобы
  • past-tense-like form

The verb here is попасть (perfective), and попал is used because Russian is expressing a desired result: preventing the sauce from ending up on the shirt.

So although попал by itself can mean got / landed, after чтобы it works more like:

• so that it does not end up getting there

Because попал comes from the perfective verb попасть, which focuses on a single completed result:

• попасть = to get into/on, to end up landing somewhere

Here the speaker wants to prevent that result:

• so that the sauce does not get on the shirt

Using попадал (imperfective) would sound less natural here, because the sentence is about preventing the sauce from ending up on the shirt at all.

So:

• не попал = doesn’t get / won’t get on it
• result-focused, which fits the meaning well

Because на can take different cases depending on the meaning.

• на + accusative = motion toward / onto something
• на + prepositional = location on something

Here the idea is:

• the sauce might get onto the shirt

So Russian uses на рубашку (accusative).

Compare:

• Соус попал на рубашку. = The sauce got on the shirt.
• Пятно на рубашке. = The stain is on the shirt.

The first is about reaching the shirt; the second is about being located there.

Because соус is the subject of попал.

In the clause:

• чтобы соус не попал на рубашку

the sauce is the thing that might get onto the shirt. So it is the grammatical subject, and therefore it appears in the nominative case.

Yes, Russian word order is fairly flexible, although some orders sound more natural than others.

The original sentence is neutral and natural:

• Когда я готовлю, я надеваю фартук, чтобы соус не попал на рубашку.

You could also say:

• Я надеваю фартук, когда готовлю, чтобы соус не попал на рубашку.

That still means basically the same thing.

Russian word order often changes for emphasis, rhythm, or style, but the original version is a very standard way to say it.

Usually рубашка means shirt.

Depending on context, it can sometimes refer to other shirt-like garments, but for a learner, shirt is the right basic meaning here.

So:

• на рубашку = onto the shirt

In this sentence, it simply means the speaker does not want sauce to get on their shirt.

Yes, this is natural Russian.

It sounds a little neat and complete, but it is absolutely normal. A native speaker could say this in real life.

More conversational variants are also possible, for example:

• Когда готовлю, надеваю фартук, чтобы не испачкать рубашку.
• Я всегда надеваю фартук, когда готовлю.

But the given sentence is correct, natural, and useful for learning several common grammar patterns.