The Roles page can be found in the administration menu under Security. The role's page lists all the roles in Continua and allows you to create, edit and delete them.
Creating a Role
Clicking the "New Role" link will pop up a dialog with all the input fields needed to create a new role.
The permissions list contains every single permission in Continua grouped by category. The permissions selected here are the ones you want the role to have access to. Take note of each category also having a check box which selects all the child permissions. If you for example select Projects then it will auto-select Create Project, Delete Project, Update Project and View Project. However, selecting Projects is an alias for Projects.*, so if a new permission was added, say Backup Project, then the role you've created will have permission for it. If, on the other hand you didn't select Projects and instead explicitly selected the Create/Delete/Update/View Project permissions then the role would not have permission to Backup Project.