kare wa houchou o aratte kara, manaita mo aratta.

は marks 彼 as the topic of the sentence: the person we are talking about.

So 彼は means something like as for him or he as the topic.

A learner may wonder why this is not 彼が. In this sentence, は is natural because the sentence is just describing what he did. が would be more likely if you were identifying him specifically, emphasizing that he is the one who did it, or answering a question like Who washed them?

を marks the direct object of the verb. In other words, it shows what is being washed.

• 包丁を洗って = wash the knife
• まな板も洗った = also washed the cutting board

So 包丁 is the thing receiving the action of 洗う.

〜てから means after doing ..., and it shows that one action happens first, then another happens after that.

Here:

• 包丁を洗ってから = after washing the knife
• then まな板も洗った = (he) also washed the cutting board

So the sentence clearly gives the order:

1. wash the knife
2. then wash the cutting board

This pattern is very common:

• 食べてから、勉強する。 = After eating, study.
• 家に帰ってから、寝た。 = After going home, slept.

This is because of how 〜てから works.

To connect a verb to から in this pattern, you use the て-form:

• 洗う → 洗って
• 洗ってから = after washing

The final verb of the whole sentence carries the tense, so that one is in the past:

• 洗った = washed

So the structure is:

• Verb in て-form + から
• then the main verb, which shows the actual tense of the sentence

That is why you get:

• 洗ってから、洗った

It does not mean one verb is less past than the other. The past meaning for the whole sentence is mainly shown by the final verb.

も means also or too.

So まな板も洗った means he washed the cutting board too, in addition to something else. In this sentence, that something else is the knife.

This creates the idea:

• He washed the knife.
• He also washed the cutting board.

A useful comparison:

• まな板を洗った = washed the cutting board
• まな板も洗った = also washed the cutting board

So も adds the meaning of in addition.

Japanese often leaves out words that are already clear from context.

In this sentence, once 彼は has been established at the beginning, there is no need to say it again in the second clause. It is understood that the same person did both actions.

So this is normal:

• 彼は包丁を洗ってから、まな板も洗った。

A more repetitive version like this would usually sound unnecessary:

• 彼は包丁を洗ってから、彼はまな板も洗った。

Japanese prefers omission when the meaning is obvious.

Yes, very often it could.

If the context already makes it clear who did the action, Japanese would commonly say just:

• 包丁を洗ってから、まな板も洗った。

That can still mean (He) washed the knife and then also washed the cutting board, depending on context.

Japanese frequently drops subjects and topics when they are understood. So 彼は is included only if the speaker wants to make the topic explicit.

It usually implies that the first action is completed before the second one happens.

So 包丁を洗ってから、まな板も洗った suggests:

• first he finished washing the knife
• after that, he washed the cutting board

This is stronger than simply listing actions one after another with just て-form, which can sometimes sound more like a simple chain of actions.

Compare:

• 包丁を洗って、まな板も洗った。
  He washed the knife, and washed the cutting board too.

• 包丁を洗ってから、まな板も洗った。
  After washing the knife, he then washed the cutting board.

The version with から makes the order more explicit.

The comma is mainly there to make the sentence easier to read and to show a pause.

Japanese commas are often more flexible than English commas. This sentence could be written with or without the comma, and both would be understandable:

• 彼は包丁を洗ってから、まな板も洗った。
• 彼は包丁を洗ってからまな板も洗った。

The comma helps separate the after doing X part from the main action that follows.

No. The particle comes after the word it attaches to.

So the natural form is:

• まな板も

not:

• もまな板

Japanese particles follow the noun or phrase they mark. Here, も attaches to まな板 and means the cutting board too.

The same principle applies to other particles:

• 彼は
• 包丁を
• 学校に
• 友だちと

Particles come after the word they belong to.

Not in exactly the same way.

〜てから is a grammatical pattern attached directly to a verb:

• 洗ってから = after washing

それから is a separate connecting word meaning something like and then or after that.

So these are different:

• 包丁を洗ってから、まな板も洗った。
  After washing the knife, he also washed the cutting board.

• 包丁を洗った。それから、まな板も洗った。
  He washed the knife. After that, he also washed the cutting board.

Both are natural, but the structure is different.

Because the knife is the first item mentioned, and the cutting board is being added as an extra item.

So the logic is:

• He washed the knife.
• He washed the cutting board too.

That is why only the second item gets も.

You could use も on both items in other contexts, but that would create a different structure or emphasis. In this sentence, using も only on まな板 is the natural way to express also the cutting board.

Yes, it is natural and straightforward.

It sounds like a normal description of two actions done in sequence:

• knife first
• cutting board second

It is also a nice example of several very common grammar points working together:

• は for topic
• を for direct object
• て-form + から for after doing
• も for also
• omission of repeated subject information in the second clause

So this is a very useful model sentence for learners.