When you create an assignment, you will be prompted to select a page range or section range (from the Table of Contents). If you would like to create a single assignment with multiple page or section ranges (e.g., read pages 40-50 and 56-58), click Add another part when creating the assignment to build a multipart assignment. Each "part" is a page or section range.
When you create a multipart assignment, students will see one part at a time and can navigate between the parts using the Continue assignment button at the bottom of each part (or the Previous part button at the top of each part).
Multipart assignments are graded as a single assignment. For example, if you require 5 comments for full credit, then students can distribute their 5 comments in any way they like among each of the parts.