Assignment feature allows instructors to give some tasks (offline activities) to learners while they are a member of a course session. Assignments are generally a reading or writing task, which would have some content items (word/pdf...) attached by the instructor, and then learners can view/download these files and attach their own completed items with their submission. One or more tests can also be included as part of an assignment. Instructor would then evaluate the work submitted by the learner and give appropriate points.
Assigning the Assignment
Assignments are not created in courses, rather they are course session specific. So each instructor can have their specific assignment for their learners. Also, assignments are not automatically assigned to all learners by default. After creating the assignment, instructors can choose to which learners they want to assign the specific assignment. This allows instructors to make personalized assignments for individuals. Assignments can also be assigned to specific sub-groups. But to address the situation where assignment is for everyone in the courseSession, you can enable course session's setting "Auto Assign Assignments", that will eliminate the need for instructors to manually assign the assignment to learners.