different users

hi:

I can send a form to SharePoint and receive it from SharePoint. But I want apply roles to my forms.For example I want send a form to user A to fill up form and then send it to another user to continue process.How can define users in my process? How can I send form from orchestration to specific user/group?Where can I define users, groups and organization chart and use them in my orchestration?I want from flow between different users in my orchestration.Thanks