simin ha kono tosyokan wo tukaimasu.

は marks the topic of the sentence.

In 市民 は この 図書館 を 使います, 市民 is the topic: you are talking about citizens and then saying what they do.

A natural way to think about it is:

• As for citizens, they use this library.
• Citizens use this library.

In many beginner sentences, は often looks like the English subject marker, but it is not exactly the same thing. It marks what the sentence is about.

を marks the direct object of the verb.

The verb here is 使います (to use), and the thing being used is この図書館 (this library). So:

• この図書館 を 使います
• use this library

A very common pattern is:

• [someone] は [thing] を [verb]
• topic + object + verb

So this sentence follows a basic Japanese word order pattern.

この means this, but unlike English this, it must be followed by a noun.

So:

• この図書館 = this library

You cannot normally use この by itself.

Compare:

• この図書館 = this library
• この本 = this book
• この人 = this person

If you want to say this one by itself, Japanese usually uses これ instead.

So:

• この
  • noun
• これ = this one

Because Japanese sentences normally place the verb at the end.

So the basic structure is often:

• topic / subject
• object
• verb

In this sentence:

• 市民 は = as for citizens
• この 図書館 を = this library
• 使います = use

This is one of the biggest differences from English. In English, you say Citizens use this library. In Japanese, the verb comes last.

使います is the polite non-past form of the verb.

Its dictionary form is:

• 使う = to use

The -ます form is commonly used in polite speech:

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

The non-past form in Japanese can refer to:

• a present habit: use
• a future action: will use

In this sentence, it most naturally sounds like a general/habitual statement: citizens use this library.

It can mean any of those depending on context.

Japanese nouns usually do not change for singular vs. plural, and they usually do not have articles like a or the. So 市民 by itself can mean:

• citizen
• citizens
• the citizen(s)

You figure out the most natural meaning from the situation.

In this sentence, citizens is the most natural interpretation.

Japanese normally does not use articles like English a, an, and the.

That means a noun like 図書館 can mean:

• a library
• the library
• libraries

depending on context.

Here, この already makes it specific:

• この図書館 = this library

So there is no need for a separate word like the.

Yes, but the nuance would change.

Compare:

• 市民 は この図書館を使います
• 市民 が この図書館を使います

With は, the sentence sounds like a statement about citizens as a topic:

• As for citizens, they use this library.

With が, the focus is more directly on citizens as the subject:

• It is citizens who use this library.
• Citizens use this library (with stronger subject focus)

For a neutral textbook sentence, は is very common.

It is grammatical and easy to understand. It means use in a broad sense.

However, depending on the situation, Japanese might also use more specific verbs, such as:

• 利用します = use / make use of
• 借ります = borrow

So:

• この図書館を使います = use this library
• この図書館を利用します = use this library/facility
• この図書館で本を借ります = borrow books at this library

Your sentence is perfectly fine for learning the structure.

The sentence is read:

• 市民 = しみん
• は = わ
• この = この
• 図書館 = としょかん
• を = お
• 使います = つかいます

So the full reading is:

しみん は この としょかん を つかいます

Two useful pronunciation notes:

• The particle は is written は but pronounced わ.
• The particle を is written を but pronounced お in modern Japanese.

Yes. That is actually the most natural interpretation.

The -ます non-past form often expresses:

• habitual action
• general truth
• future action

So this sentence usually means something like a general statement:

• citizens use this library
• citizens make use of this library

It does not necessarily mean they are using it at this exact moment.

If you wanted to stress an action happening right now, Japanese would often use a different form, such as 使っています.

Japanese normally does not use spaces between words.

So this sentence would usually be written as:

市民はこの図書館を使います。

Spaces are often added in beginner materials to help learners see the parts of the sentence more clearly:

• 市民
• は
• この
• 図書館
• を
• 使います

So the spaces are for learning convenience, not standard writing.