Потом она положила второй корж сверху.

Потом means then, after that, or next. In this sentence, it links this action to the previous step, which is very common in instructions, recipes, and storytelling.

So Потом она положила... is basically Then she put...

Because the subject is она meaning she.

In the Russian past tense, the verb agrees with the subject’s gender and number:

• положил = he put
• положила = she put
• положило = it put
• положили = they put

So with она, you need положила.

Положила is the perfective form, so it presents the action as completed: she put the layer down as one finished step.

That fits recipe-style narration very well, where actions are listed one by one:

• first she did X
• then she did Y
• then she did Z

Клала is the imperfective past of класть, and it would sound more like an ongoing, repeated, or process-focused action.

Also, the standard verb pair is:

• класть = imperfective
• положить = perfective

English speakers often notice forms related to ложить, but in standard Russian, положить is the normal perfective partner of класть.

It is in the accusative case because it is the direct object of the verb положила. It is the thing she put.

However, for a masculine inanimate singular noun, the accusative looks the same as the nominative. So:

• nominative: второй корж
• accusative: второй корж

That is why the form does not visibly change here.

Because второй has to agree with корж.

Корж is:

• masculine
• singular
• inanimate

So the adjective must match it:

• второй корж = second cake layer

If the noun were feminine, you would get вторая. If it were neuter, второе.

Корж usually means a cake layer, sponge layer, or a baked flat round layer used to build a cake.

So it is not the whole cake. It is one layer of the cake.

In this sentence, второй корж means the second cake layer.

Here сверху means on top.

So положила второй корж сверху means she placed the second cake layer on top of something already mentioned or understood from context, probably the first layer.

A useful point: сверху can also mean from above in other sentences, but here the meaning is clearly on top.

Russian often leaves out information that is obvious from context.

Here, the listener probably already knows she is assembling a cake, so сверху naturally means on top of the first layer or on top of it.

If you wanted to say it more explicitly, you could say something like:

• сверху на первый корж
• сверху на него

But in a recipe or step-by-step description, the shorter version is very natural.

Because these words are not quite the same.

• наверх usually means upward or to the top
• сверху usually means on top or from above

In this sentence, the important idea is the final position of the layer: it ends up on top of another layer. So сверху is the natural choice.

No, Russian word order is fairly flexible.

Потом она положила второй корж сверху is a natural, neutral way to say it in narration or instructions:

• Потом sets the sequence
• она gives the subject
• положила gives the action
• второй корж is the object
• сверху adds where it went

You could rearrange the sentence for emphasis, but the given order sounds very normal and clear.

The stress is:

• потОм
• онА
• положИла
• вторОй
• корж
• свЕрху

Stress matters a lot in Russian, so it is worth learning each word together with its stressed syllable.