In Canvas, you can easily add new users into your course in addition to those that are added automatically. Do this by using the "+ People" button on the People tab as seen
Students have the ability to submit assignments and interact with the course. Students have restricted permissions, but they have enough permissions to use Canvas.
Teachers are course admins and have full control over the course.
TAs are very similar to teachers in the sense of permissions, except TAs do not have access to add or remove Teachers, TAs, Designers, or Graders.
Designers have access to create and edit course content, discussions, announcements, assignments, quizzes, and other content features. Designers cannot access grades. If users also need access to input grades, they should be listed as TA instead.
Graders have access to grades and assignments within a course, but will not have access to modify other course content. If users also need to access or modify course content, they should be listed as TA instead.
Observers are non-participating guests that can be added to a course. This role allows a user to see course content without allowing the user to participate in the course.
Communicators have the ability to manage communication within a course. They can send messages to the entire class, post announcements, and moderate discussion boards. This role can be added to an existing role like Student to provide select class leaders with greater responsibility within the class.