This dialog appears when you convert an empty column into a factor and lets you specify the number of factor levels and any associated labels or numerical levels.
Number of levels
The number of groups or classes that the factor will index.
Levels and labels
Edit the numerical values and/or text labels associated with each group/class in the factor.
See also
Understanding Factors within a Spreadsheet
Edit Factor Levels and Labels dialog
Change Factor Levels and Labels dialog
Reorder Factor Levels
Recode a Column
Spreadsheet Factor Menu
Split a Text Column
Combine/Concatenate Text Columns