haha wa suupu ni koshou o kakemasu.

は marks 母 as the topic of the sentence: As for mother, ...

So 母は means something like:

• Mother ...
• As for my mother, ...

In natural English, we usually just say Mother puts pepper on the soup or My mother sprinkles pepper on the soup.

A useful point: 母 by itself often means my mother when talking about your own family to someone else.

Because かけます takes two different roles here:

• こしょうを = the thing being applied/sprinkled/poured
• スープに = the target thing it is put onto

So the structure is:

• X に Y を かける
• to put/apply Y onto X

In this sentence:

• スープに = onto the soup
• こしょうを = pepper
• かけます = puts/sprinkles/applies

So literally it is close to:

• Mother applies pepper to the soup.

かけます has several meanings depending on context, so learners often find it confusing.

Common meanings include:

• to hang
• to wear (glasses, etc.)
• to call (on the phone)
• to pour over / sprinkle / apply onto

In スープにこしょうをかけます, it means:

• to sprinkle pepper onto
• to put pepper on

So this is not the phone call or wear glasses meaning. The particles and the nouns around it tell you which meaning is intended.

Because with this verb pattern, the soup is treated as the destination/target surface, not the direct object.

Compare the roles:

• スープに = onto the soup
• こしょうを = the pepper being added

Japanese often marks the place or target of an action with に.

If you think of it as apply pepper to soup, the particle choice makes more sense.

Yes, but the nuance changes.

• 母はスープにこしょうをかけます。
  As for my mother, she puts pepper on the soup.
  This sounds like a neutral statement about the topic.

• 母がスープにこしょうをかけます。
  My mother is the one who puts pepper on the soup.
  This gives more focus to mother as the subject.

So は is more topic-setting, while が is more subject-focused or contrastive depending on context.

When talking about your own mother to someone else, Japanese usually uses the plain family term:

• 母 = my mother
• 父 = my father

When directly addressing your mother, or when referring to someone else’s mother more politely, Japanese often uses:

• お母さん

So in this sentence, 母 is the normal choice if the speaker is talking about their own mother.

こしょう / コショウ / 胡椒 means pepper.

It is often written in katakana as コショウ, especially in everyday writing, menus, recipes, and labels, because food items and plant names are often written that way for readability.

Here it is written as こしょう in hiragana, which is also possible.

So:

• こしょう
• コショウ
• 胡椒

can all refer to pepper.

Japanese basic sentence order is often described as:

• topic / subject + other information + verb

So unlike English, the verb usually comes at the end.

This sentence is arranged like:

• 母は = topic
• スープに = target
• こしょうを = object
• かけます = verb

That final-verb pattern is very normal in Japanese.

かけます is the polite non-past form of かける.

That means it can mean either:

• puts / sprinkles
• will put / will sprinkle

depending on context.

So:

• dictionary form: かける
• polite form: かけます

In a textbook sentence like this, ます is used because it is the standard polite form learners study first.

By itself, かけます can describe either:

• a habitual action: Mother puts pepper on her soup
• a future action: Mother will put pepper on the soup
• sometimes a present action in certain contexts

Without more context, many learners will understand it as a general/habitual statement.

So depending on the situation, it could mean:

• My mother puts pepper on soup.
• My mother is going to put pepper on the soup.

Context decides which one is most natural.