lease follow below steps to create accounts for your clients in WHM.
1) Login to WHM (http://your_ip:2087 )
2) Create package by clicking on "Add Package" link in packages category.
While creating packages do not put "UNLIMITED" in any feature field box as WHM treats "UNLIMITED"= 1. You may face some problems in future if you put "UNLIMITED". Hence Always assign some reasonable number say 999 or 9999 for UNLIMITED.
3) Then click on "Create New Account" in Account Functions Category. Enter domain name , user name and password. Then select package you want to associate with particular account and hit "Create" button.
Please wait until you see message "Account creation completed". This may take a bit longer some times due to multiple DNS entries being added.
That's it.. :) you are now ready to use newly created account.
Note: You need to update newley created domain DNS to your reseller account servers. It means your reseller domain and all your clients domains points to same name server.
After DNS propagation you can access newly created domain cPanel just like your domain. http://www.domain.com/cpanel
If your client domain is under DNS propagation you can still access control panel using http://Server_Ip:2083 and enter client domain user name and password.
"Server_Ip" is the ip of your main account which was sent to you in the setup mail.