A "reservation" is an agreement that you will be allowed to use something at a certain time and on a certain day. Some things that you can reserve include:
- a table at a restaurant
- a hotel room
- tickets for a flight
- a conference hall
A "reservation" is similar to an appointment, except that an "appointment" is with a person, while a "reservation" is for a location or an object.
When you want to reserve something, you first "make" a reservation by calling or emailing the owners or filling out an online form. After you "make" the reservation, you "have a reservation".