The Torch:

The torch is lighted using the rays of the Sun by a parabolic reflector at the site of the Ancient Olympics in Olympia, Greece. The torch is then taken out of Greece to the main stadium where the cauldron is lighted on the final day/opening ceremony. This torch is left to burn till the games have been officially closed.

There are interesting stories about so many Olympic Relays.
In 1976 Summer Olympics(Montreal), the flame was transmitted “electronically” via satelite from Athens to Ottawa, by means id an electronic pulse derived from the actual burning flame. After a rainstorm doused the Olympic flame, an official relit the flame using his cigarette lighter. Organizers quickly doused it again and relit it using a backup of the original flame.

A lot of money goes into designing of the Olympic Torch. They have to withstand wind speeds up-to 65 km/hr, rain upto 50mm an hour. Other requirements are that the design should be such that it can be identified and photographed in sunshine and areas of extreme brightness. The fuel is propane which is in accordance with environmental guidelines. The material of its form is recyclable. For Sydney 2000, there was a special requirement since it had to be kept submerged in water.
WOW: I never thought that Science and Technology would help us in such ways.The final carrier of the torch is often kept secret until the last moment, and is usually a sports celebrity of the host country.

Some more facts:
The torch has been carried by an airplane in 1952, when the fire traveled to Helsinki.
The Torch Relay symbolizes the passing of Olympic traditions from one generation to the next.

Facts from : Wikipedia