In addition to Todoist's usual Priority values (1, 2, 3, 4), the Priority column can also contain these special values:
Add the following tasks to a Todoist section with the name given in the first Tasks columns.
If the section does not already exist, it will be created.
To add further tasks that are not assigned to a section, create a new unnamed section.
Exclude this row when importing.
Pro tip: utilize the power of spreadsheets to exclude rows if certain conditions are met.
For example, a cell in the priority column could contain something like: =IF($J$3="No", "x", "2")
In this case, if J3 contains a value of No, this task would not be imported; otherwise it would be imported with priority 2.