Once you show up at the appointment, you will fill out a piece of paper explaining who you are, how many times you have been there (i.e. This is my 3rd appointment), who your case worker is, and your nationality - and then sit and wait.  Assuming you are on time, your case worker should come out shortly and guide you into an interview room. 

Actually, "Booth" is probably a more appropriate term, as the room is small and conversations can be heard between neighboring rooms.  Your case worker will ask you some preliminary questions, give you a pamphlet, and then prepare a listing of all of the supporting documentation you will need for your application.

The purpose of the questions is probably three fold:

1. To determine whether you can communicate (in Japanese) and are sane.

2. To make sure you know what you are doing and understand the implications.

3. To determine what documentation you will need, and whether you will reasonably be able to obtain it.

The documentation required differs from nationality to nationality and person to person.  For example, Korea has something similar to Japan's Family Register that they can request, while for Americans, they will need to instead request a number of Birth Certificates, Marriage Certificates, etc.  Also, they may request notes from your parents, etc. - but that's not possible if they are already deceased.  

After hearing your story, your case worker will review the requirements with you and discuss what each item is and how to request it (for domestic items only, of of course).  If everything is in order, you take your documents and go home.  You should probably schedule your next appointment for a month or so later when you leave.  If you don't, you can always schedule an appointment by phone later - but beware that sometimes the next available appointment may not be until several weeks later.