Parameter 2 is the secondary, or field, delimiter. This allows you to select groups within groups. For example, to sort by specific items within a line, you would pass "," for parameter 2 and the return character for parameter 3.
Data from a spreadsheet would typically be formatted with the rows separated by returns and the columns separated by tabs. In that case you would pass tab for parameter 2 and return for parameter 3.
If you wanted to sort words within items, you would pass space for parameter 2 and "," for parameter 3.