appointment / reservation / plans

So, today I'm going to be clearing that up for you. Let's have a look.

그래서 오늘 그걸 정리해드리려고 해요. 한번 살펴볼까요?

[plans] you have arranged to do something with someone on a special day or at a specific time.

I have plans tonight. I've made plans with her. Do you have any plans for the weekend? Sorry, I can't come out today because I've made plans with my brother.

[appointment] meeting with a person or people in a professional setting.

I'd like to make an appointment with Dr. John, please. I have an appointment with my lawyer at 2 p.m.

[reservations] Arrangement in which something physical, for keeping a seat, a table and a room.

I'd like to reserve(=make a reservation for) a table for two at 9 p.m tonight. I'll reserve two ticket for Mamma Mia tomorrow night. I'd like to book(=make a booking for) one of your rooms next week, please.

Make sure that you always use the plural form 'plans'.

make sure that ~ : ~을 명심하세요.