It all starts in Conan's village, as a young boy living with his father and mother. One day, the village is ransacked then destroyed, Conan loses his father to wild dogs, and then has his mother's head chopped off while he is holding her hand. All he remembers from the event is the standard of the warriors - that of two snake heads, joined at the body, facing each other over a moon. This is the standard of Thulsa Doom(James Earl Jones), who is the master villain in the first movie. Conan is then sent into slave labor with several other young boys. He is condemned to the "Wheel of Pain", a giant wheat grinder that operated off of humans pushing on its spokes. At first, Conan is one of many pushing the wheel, but in the end, he is the only one that survives, and is the only one pushing the wheel, all by himself...
You see, Thulsa Doom, by condemning Conan to the "Wheel of Pain", instead condemned himself to die. Conan used the situation, no matter how crappy it appeared, to get stronger - to feed his thirst for revenge for the murder of his people, including his immediate family. Conan fought back, when there was nothing worth fighting for.
Anyway, Conan is taken to the Gladiatorial Arenas, where he learns to use his might to kill humans for pleasure. After his victories "could not easily be counted", he is taken to train in the East with master oriental swordsmen. He learns well, and is now a complete warrior.
Watch the movie to find out the rest...