The sort order determines the order the entries are printed on the report.

Entry Select Entry if you want to print the entries in the order that they were entered (reference number).
Transaction Code Select Transaction Code if you want to sort the entries by transaction code and print a subtotal for each transaction code. The entries for each transaction code will print in chronological order.
Date Select Date if you want to sort the entries by transaction date and print a subtotal for each date. The entries for each transaction date will print in entry order.