LDAP Tools
There are some tools in the LDAP directory (icewarp/ldap) that help to administer LDAP DB. The tools have the same parameters as the tools of the OpenLDAP project.
slapadd
Slapadd allows you add records to LDAP DB using the LDIF format. You can see an example in the LDAP directory. The two files, create.ldif and create.bat, create the suffix in the LDAP DB using the slapadd tool. Similarly you can add more records by editing the create.ldif file. Syntax of the LDIF format can be found on the Internet.
schema
The LDAP schema, as with all database schemata, is the definition of what can be stored in the directory. The basic thing in an entry is an attribute, like given Name. Each attribute is associated with a syntax that determines what can be stored in that attribute (plain text, binary data, encoded data of some sort), and how searches against them work (case sensitivity, for example). An object class is a three tuple, consisting of (must have, required, may have), saying what other attributes can or should be present.
There is a standard core of schema definitions (object classes, attributes and syntaxes), and you can define your own to suit your particular needs. Most every organization will want to do that.