Once your reseller account is setup and you have access to WHM you will need to add your customer hosting accounts.  
This will create a hosting account which will provide the client with access to their CPanel and all the web and email hosting. 

• Log into WHM

• From the dashboard click "Account Information - List Accounts".  This will display a list of your hosting accounts.  If you have just started then this list will be empty.
• Click Home to take you back to the dashboard.
• Click Account Functions -> Create New Account

• Fill in the fields with the following information (Domain, Username, Password and a contact Email) : The username will be generated for you but you can choose one of your own. 
• Select a Package 
• For all other settings the default can be used. 
• Click the Create button.