What is?
This pose is named after the Hindu mythological warrior Virabhadra and is consequently referred to as the warrior pose. The pose has two varieties, Virabhadrasana I and Virabhdrasana II, both having slightly different foci and building different parts of the body.

Virabhadrasana I stretches the legs while helping open up the chest and hips. VirabhadrasanaII helps build up the lower torso and expands the chest while improving deeper breathing.

What is the technique of practicing it?
The Virabhadrasana I pose starts off with the feet splayed as far apart as is possible while maintaining stability. The heels should be in line with each other as the arms are brought up at inhalation. Once the arms are up above the head, the right foot should be turned at a 90 degrees angle and the left foot in at a 45 degrees angle. The legs should remain straight and the heels should be rooted while the shoulders pressed down and the chest open. Then the body should be turned to the right but the feet should remain in the same position. After holding this position for a few breaths, the right knee should be bent so that the thigh is parallel to the ground. Once this position is attained, the person can go back to the original position retracing the steps. 

Virabhdrasana II starts off from the Virabhadrasana I position as the arms are raised to shoulder level. After inhaling the head is turned to the right and held. Exhaling, the right knee should be bent and brought over the right heel. This position should be held for up to 8 breaths after which the person should return to the original position