Thenmadurai Vaigai Nadhi seems to be a song or a music piece, possibly from a Tamil movie or album. I'm assuming it's a popular or iconic tune that you'd like to set as your ringtone.
You're looking for information on downloading a ringtone, specifically "Thenmadurai Vaigai Nadhi". Here's what I found: Thenmadurai Vaigai Nadhi Ringtone Download