The Twins
Gemini is one of the larger constellations in our sky and also has, along with most of the other constellations, very interesting mythology. Although the Gemini is called "The Twins" and actually resembles a set of twins in the sky, these twins actually had different fathers.
The twins in this case are Pollux and Castor, which are the stars that represent the heads of the twins. The twins' mother was Leda, Castor's father was Tyndareus, who was the mortal king of the ancient Greek city of Sparta. Pollux's father, on the other hand, was the Greek god Zeus.
This resulted in the very unusual situation where Castor was mortal and Pollux, being the son of a mythological god, was immortal.

When Can I See Gemini?
It should be easy to find Gemini any time that Orion is visible. Using the chart we have provided at the right, you can see that the Twins are located above and to the right of Orion's right shoulder. Like Orion, Gemini is visible in the early morning hours during the late fall and early winter. It is overhead during the winter months. Once you have found the stars Castor and Pollux, the stars which are the "heads" of the twins, seeing the rest of the constellation should be easy.