Before creating your first account you will need to create a default package via the WHM ‘packages’ menu. A package is an account template containing details on the amount of disk space, data transfer etc. to assign to an account. You can create as many packages as you need (e.g. one for each of your different hosting plans) but you must have at least one added before you can begin creating accounts.
Once you have created a new default package you will be able to use this package when creating a new account. You can still, however, make adjustments to the disk space and data transfer quotas when creating new accounts.
For a tutorial on creating a hosting package please refer to the following KB article: Creating Custom Packages in WHM
Moving along, once your package is created, you can proceed with creating an account as outlined in the following video tutorial: