Detail on ldap_servers' configuration

Hello guys:
I’m a new-fish on LDAP’s configuration. When I saw gitlab_rails[‘ldap_servers’] items on gitlab.rb, I hardly can mapping the section into LDAP’s conception. Can someone gives me a help on that? With highly appreciate!

The sections are:
uid:
bind_dn:
base:
user_filter:
What does these four sections mean? Do I need to fill them all or some of them can be blank

B.R