To run Tptime, just be sure the program is in your PATH, and type "tptime" in any Terminal.
If you have installed the rpm for Mandrake, the TPtime icon should appear in the main menu in section Applications/Sciences/Other.
Normally, a beautifull GTK window should appear in the center of your screen :)
Nothing difficult here: fill the entry corresponding to your date format, and click on the juxtaposed button to obtain the same date in all other formats.
See the "Date format" section to have a more precise description of available date formats.
On this page, you can see a calendar which indicates you the position of the converted date in the corresponding month on a Gregorian calendar.
You can see also if it a leap year or not.
Note: I use for this the GtkCalendar widget, but i don't know the limits of the algorithm used to display the name of the day corresponding to the Gregorian date, so be carefull with this result.