How to cinfigure openLDAP (server as well as client)

I got this error [Error downloading CA certificate] while clicking download CA certificate. I am following book, RED HAT SYSTEM ADMINISTRATION II, Chapter 8, Page # 158. It pop up after clicking marking Use TLS to encrypt connections.
Any help is highly appreciated.

Hi Sufian,
as your topic is quite wide I want to throw in an blog article I found very useful when getting first insights about openldap - It is from a german company that uses openldap in their open source product: