Assignment groups are used to gather similar types of assignments together, and to give them a grade as a group.  If you want to use them, go to the Assignments tab in your course. Click Add an assignment group.

Assignment groups

When you start, the Other assignment group carries 100% of your grade weight. As you create your own assignment groups, you will redistribute that weight from other to your groups. You can distribute the full 100% throughout your own assignment groups or leave a remainder in Other to cover miscellaneous assignments or grading factors.

1. Give the group a name (“Quizzes”, “Tests,” “Labwork,” etc.).
2. Enter the Weight (from 0-100).
3. Check if every assignment in this group should be Extra Credit.
4. If you wish to drop the lowest-graded assignments from a student's final grade calculation, enter the number of assignments to drop.
5. Click Save to finish.

https://support.populiweb.com/hc/en-us/articles/223797467 

Populi Step Two: Set Up Assignments

Assignments

1. Give the assignment a name, description, and number of points.
2. Check if this is an extra credit assignment.
3. Select an assignment group.
4. Select the assignment type.
   • If you select Test, fill in the additional test fields (read more about these here).
   • If you select Discussion, choose whether to create a New discussion or select from existing discussions.
5. Enter a due date/time.
6. By default, your students can see this assignment before the due date; uncheck Visible if you wish to surprise them with it (great for pop quizzes!).
7. Click Save to finish. 

As you add assignments, they will list arranged by due date; click the column headings to sort the table differently.

Each assignment type lets you and the student comment back and forth (and even attach files to the comments).

• Grade-only: Just give the student a grade. It's good for things like readings and other simple assignments that don't require a lot of interaction.
• File: Requires the student to submit a file to you for evaluation; good for essays, papers, etc. that benefit from feedback, revisions, and other interaction.
• Test: Creates a corresponding online test.
• Attendance: Calculates an assignment grade based on the student's attendance at course meeting times.
• Discussion: Creates a corresponding discussion.
• Essay: These provide students with a WYSIWYG editor that they can use to compose and format an essay-length composition right in Populi.
• Peer Review: Peer-review files and essays let other students in the course section view, comment on, and even grade the student's work. Read more about peer-review assignments.

You can attach any kind of assignment to a Lesson.