Open the WHMCS product page and go to Module Settings. Select VPS at Server Type and configure the ressources.
The Override ACL Group option let you override the default ACL group which has been setted at the module configuration. This feature can be used, for example, to sell managed VPS with limited permissions.
Next assign the hostsystem to the appropriate IP subnets. Open the IP Manager at the module admin page and click Configure Pool.
Ensure that you have enabled the auto setup at the WHMCS product configuration. When a new order arrives, the VPS will be created automatically.