When you click on Setup->Service or Setup->Personal Reason, you'll see the option to add either on both screens. So what is the difference?
Personal Reasons are entered in association with Holidays or Vacations you may add the Main->Holiday/Vacation. Your clients will never see the personal reasons you've added, but they will not be able to book during the times you've selected to be on holiday or vacation.
You can find out how to add vacations for a specific location by accessing the documentation found here and how to add holidays for a specific staff member or members by accessing the documentation found here.
Services are entered as the appointments clients can book with you. Your clients will see all of these items on your scheduler based on the location they are offered in. You can find out a lot more about services here.