The Assignments tool in Canvas allows an instructor to create and track all of the assignments in a course and shows students all of the activities that will be expected of them and the points for each activity.
In Canvas, gradebook set-up is contingent on the creation of assignments and assignment groups. It is fairly accurate to say that in Canvas, Assignments and Gradebook are different aspects of the same tool.
All gradable items, such as assignments, discussions and quizzes can be created directly in Assignments. You can also create quizzes and graded discussions in their own tool; each item will show up as an assignment.
See the Canvas Instructor Guide for addtional guides on Assignments and Grades.