Cascade's system is based on the hierarchy that exists in your organization. The structure begins with your overall Organization at the top, and then branches into smaller sub-sections called “Organizational Units”. Having Units allows you to create multiple plans (one for each of your departments perhaps) and group Roles into specific divisions of your organization.
“Organizational Units” are not the only hierarchy in Cascade. Roles also follow a hierarchical system, and because users are placed into each of these roles they are subsequently placed in a hierarchy. The hierarchy makes it easier for users to see goals within your plan that relate to them and their team.
There is a 1:1 relationship between Roles and Users in Cascade, meaning every user created must sit within an individual Role. So, even if two people perform the same role in your organization (e.g. you have two Account Managers), you must create two Roles with the same title and assign one to each User. This is because Goals are assigned to Roles in Cascade's system (which is super helpful down the line when you may need to reassign ownership of Goals to a new user).
Read more here for Setting up Organizational Units or Adding Roles in Cascade.