The Accounts View shows you all client accounts and subpartner accounts. From this view, you can add and delete those types of accounts. Additionally, you can create an installer link for an account or you can apply an email notification or software preferences template.
The Group View allows you to group computers into logical organizational units regardless of which client account they are associated with. You will always start with a single group called the Default Group. This group can never be deleted. You can create other groups like Laptops or Desktops and apply templates to them. You can drag and drop computers to move them from one group to another.