hurimaapuri wo tukaimasu.

フリマアプリ is a compound noun:

• フリマ = short for フリーマーケット (flea market)
• アプリ = app

So フリマアプリ means a flea market app, usually an app where people buy and sell secondhand items.

Katakana is commonly used for:

• foreign loanwords
• modern technical words
• brand-like or trendy terms

Both parts of フリマアプリ come from loanwords or abbreviated modern vocabulary, so katakana is natural here.

を marks the direct object of the verb.

In this sentence:

• フリマアプリ = the thing being used
• 使います = use

So を shows that the flea market app is what the speaker uses.

Historically, を was pronounced more like wo, but in modern standard Japanese it is usually pronounced simply o.

So:

• written: を
• pronounced: o

This is very normal, and learners just memorize it as the object particle.

使います is the polite non-past form of the verb 使う (to use).

So:

• 使う = plain form
• 使います = polite form

Japanese often uses the polite -ます form in neutral everyday speech, especially in textbooks, with strangers, coworkers, customers, and so on.

使います is non-past, which means it can refer to:

• a present habit: I use flea market apps
• a future action: I will use a flea market app

Japanese non-past forms often cover both present and future, and the exact meaning depends on context.

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

So フリマアプリを使います。 could mean:

• I use flea market apps
• He/She uses a flea market app
• We will use a flea market app

In real conversation, the speaker, previous sentences, or situation usually make it clear.

Japanese normally does not use spaces between words.

So this sentence would usually be written as:

フリマアプリを使います。

Spaces are often added in beginner materials to make the sentence easier to read and to show word boundaries.

Yes. Japanese nouns usually do not change for singular and plural.

So フリマアプリ can mean:

• a flea market app
• flea market apps in general

The context tells you which is meant.

Yes. The verb is usually written with kanji as 使います.

So:

• hiragana: つかいます
• mixed writing: 使います

In normal Japanese writing, the kanji version 使います is much more common.

You could, but it changes the nuance.

• フリマアプリを使います = simply states that someone uses the app
• フリマアプリは使います = puts フリマアプリ in contrast or as the topic, something like As for flea market apps, I do use them

So を is the most straightforward choice here.

The plain casual version is:

フリマアプリを使う。

In conversation, it could also appear as:

フリマアプリ使う。

The version with を is grammatically complete, while dropping particles can happen in casual speech.

Here are the common forms:

• フリマアプリを使います。 = I use / will use a flea market app
• フリマアプリを使いません。 = I do not use / will not use a flea market app
• フリマアプリを使いました。 = I used a flea market app
• フリマアプリを使いませんでした。 = I did not use a flea market app

This follows the standard -ます verb pattern.