To add people to your course, select "People" in the left navigation menu. Click the "Add People" button and enter the SFU ID of the person you want to add. You can add multiple people by separating each ID with a comma. Under the "Role" drop-down, you get the option of adding a student, teacher, TA, designer, or observer. 

If you select "TA" as the role, under the "Section" drop-down, you can assign a section. You can restrict the TA to grade students in their section only by clicking the checkbox. Then click "Next," and Canvas will validate those SFU IDs. Click "Add Users," and Canvas will verify that these users have been added to the course. Click "Done," and those people will be added to the list of people in your course with a pending sign next to their name until they've accepted the invite to the course.