The sections.csv identifies classes in your organization. Each class in your organization will be assigned a Section ID in your file. Typically, your school informations system will assign section IDs for each class. If your information system does not, it is important to use section IDs that will be remembered in subsequent roll outs throughout the year and year-over-year.
The sections.csv is required to perform a roll out for your organization. This is crucial to student user creation.