Once you have your LiveJournal server tuned and tweaked, you're probably going to want to create some users and communitiies.
Creating users is relatively simple, and depends on which options you are using in your cgi-bin/ljconfig.pl.
If you are not using this file for your setup, then the default options defined in cgi-bin/ljdefaults.pl will be assumed.
If your service is live, simple visit create.bml in your htdocs/ directory. With this page, you can create as many users as you'd like.