The structure is how many layers will your course be divided into. for example: a 2-layer structure will divide your course into a main layer and a sub-layer (main layer could be chapter, sub-layer could be section). A 3-layer structure will add another sub-layer under topic (such as topic), and a 4-layer structure will add one more sub-layer under topic (such as unit). With a 4-layer structure, you will have your course divided into chapters, that are divided into sections, divided into topics, and finally divided into units)
In the course creation process, here are the steps to assign the course structure:
Assign the structure (2, 3, or 4 layers)
Choose a structure division name available, or create a new one of your choice
Click on "Assign"
Next Steps: