kyariikeesu wo tukau.

Because キャリーケース is a loanword-style term. Katakana is commonly used for:

• foreign loanwords
• onomatopoeia
• emphasis
• some brand- or product-like terms

Here, キャリーケース sounds like an English-derived word, so katakana is the natural choice.

They are very similar, and in many situations they overlap.

• キャリーケース usually suggests a suitcase or travel case that you pull/roll, often with wheels and a handle.
• スーツケース is also suitcase, and is a very common general term.

In everyday Japanese, people may use both for rolling luggage, but キャリーケース can feel a little more specifically like rolling luggage.

を marks the direct object of the verb.

So in:

• キャリーケースを使う

the thing being used is キャリーケース.

A very literal breakdown is:

• キャリーケース = carry case / suitcase
• を = object marker
• 使う = to use

So it means to use a carry case / suitcase.

This is just how Japanese spelling works for this particle.

• As a particle, を is pronounced o
• Historically it was distinct, but in modern standard Japanese it is usually pronounced the same as お

So learners often see it romanized as o, even though it is written を.

Because Japanese is typically a subject-object-verb language.

English often goes:

• I use a suitcase

Japanese usually puts the verb last:

• I / suitcase / use

In this sentence, the subject is simply omitted because Japanese often leaves out information that is already clear from context.

使う is the dictionary form of the verb.

This form is used for:

• plain/casual statements
• dictionary entries
• future or habitual actions depending on context
• modifying nouns
• various grammar patterns

So キャリーケースを使う。 is a plain-style sentence. Depending on context, it could mean things like:

• I use a carry case
• I’ll use a carry case
• to use a carry case

Yes. 使う is plain form, so the sentence sounds neutral/plain rather than polite.

The polite version would be:

• キャリーケースを使います。

Use the polite form in formal situations, with strangers, customers, teachers, and so on.

Yes. Japanese very often omits the subject when it is understood from context.

So キャリーケースを使う。 is perfectly normal as a standalone sentence if the context makes the subject clear. It could mean:

• I use a carry case
• We use a carry case
• They use a carry case

Japanese relies heavily on context for this.

It is pronounced tsukau.

A rough breakdown:

• つ = tsu
• か = ka
• う = u

So: tsu-ka-u

Be careful not to pronounce it like sukau. The tsu sound is important.

In very casual speech, particles are sometimes dropped, especially when the meaning is obvious. So you may hear:

• キャリーケース使う

However, for learners, it is best to keep using を until you are comfortable with natural particle omission. The full form:

• キャリーケースを使う is clearer and more standard.

By itself, it could be either. The plain dictionary form 使う does not force only one interpretation.

Depending on context, it can mean:

• a general habit: I use a carry case
• a future/intended action: I’ll use a carry case

Japanese often leaves this to context, time words, or surrounding sentences.

Yes, but it depends on the situation.

As a simple sentence, it is grammatical and natural. In real conversation, though, Japanese often includes more context, such as:

• 旅行ではキャリーケースを使う。 = I use a carry case when traveling.
• 今回はキャリーケースを使う。 = This time, I’ll use a carry case.

So the short sentence is fine, but in actual speech it often appears with extra context.