hoeuisireun yeyakjero iyonghapnida.

회의실 means meeting room or conference room.

The particle 은 is the topic marker. It sets 회의실 up as the thing being talked about:
As for the meeting room(s), ...

In a notice like this, 은 often sounds natural because the sentence is giving information about the meeting rooms in general. It is less about identifying a subject and more about stating a rule or policy.

So 회의실은 예약제로 이용합니다 is something like:
As for the meeting rooms, they are used on a reservation basis.

Korean often does not mark singular vs. plural unless it is important.

So 회의실 can mean:

• the meeting room
• meeting rooms
• the meeting-room facilities

In a notice like this, it usually refers to meeting rooms in general, so English often translates it as meeting rooms even though the Korean noun itself is not explicitly plural.

예약제로 comes from:

• 예약 = reservation, booking
• 제 = system, method, scheme
• 로 = by, through, under, in the form of

So 예약제 means a reservation system or reservation-only system, and 예약제로 means:

• by reservation
• on a reservation basis
• under a reservation system

This is a very common expression in signs and notices.

Here, -로 shows the method, basis, or system under which something is done.

So 예약제로 이용합니다 does not literally mean use it with a reservation in a simple mechanical sense. It means the facility is used according to a reservation system.

You can think of -로 here as meaning:

• by
• under
• on the basis of

So the nuance is:
The meeting rooms are used under a reservation system.

Both can relate to using something, but they are not always identical.

• 사용하다 = to use, often for tools, objects, equipment
• 이용하다 = to use, make use of, avail oneself of; very common for facilities and services

Because 회의실 is a facility, 이용하다 sounds especially natural. In public notices, 이용하다 is extremely common for places such as:

• libraries
• meeting rooms
• parking lots
• public facilities

So 회의실은 예약제로 이용합니다 sounds like a standard facility-use notice.

Yes, the subject is omitted, which is very normal in Korean.

The sentence does not explicitly say:

• you use
• people use
• employees use

Instead, it states a general rule or policy. In English, we might naturally supply something like:

• Meeting rooms are available by reservation
• Meeting rooms must be used by reservation
• Please use meeting rooms by reservation

So the sentence is less about a specific person acting and more about the general rule for usage.

The normal interpretation is reservation only or on a reservation basis, not merely preferred.

In other words, the usual implication is:

• you should reserve first
• use is managed through bookings
• walk-in use is probably not the intended system

Depending on context, a natural English rendering could be:

• Meeting rooms are available by reservation only.
• Meeting rooms must be reserved before use.
• Meeting rooms operate on a reservation system.

이용합니다 is the formal polite style, often called the 합니다-style.

This style is very common in:

• signs
• notices
• public announcements
• workplace rules
• official instructions

It gives the sentence a formal, neutral tone. A sign or office notice would commonly use this style rather than a casual ending.

Grammatically, it uses the active verb 이용합니다 (use), but in context it often feels like a policy statement rather than a straightforward active sentence.

That is why English may translate it more naturally as:

• Meeting rooms are used on a reservation basis
• Meeting rooms are available by reservation
• Meeting rooms must be reserved before use

So while the Korean is not explicitly a passive construction, English often uses passive wording to sound natural in a notice.

Yes, that is close to the literal structure.

A more literal breakdown is:

• 회의실은 = as for the meeting room(s)
• 예약제로 = on a reservation basis
• 이용합니다 = use / are used

So a literal gloss might be:
As for meeting rooms, they are used on a reservation basis.

But in real English, a notice would usually be phrased more naturally as:

• Meeting rooms are available by reservation only.
• Meeting rooms operate on a reservation system.

Yes. Even though it looks like a statement, in a notice it can function like an instruction or rule.

Korean often uses polite declarative sentences to express:

• rules
• guidelines
• official policies

So depending on context, this sentence can imply:

• Please use the meeting rooms by reservation.
• Meeting rooms should be used by reservation.

This is a common feature of Korean notices: a plain-looking statement can carry the force of an instruction.