Tadasana ( Mountain Pose) is the foundation pose for all yoga poses. It teaches us  how to activate the body for proper alignment. It stacks the bones correctly and maintains the natural curve of the spine. This in turn creates a sense of stability and imprints a sense of balance and symmetry in the body. This pose promotes  stillness, strength and power that is associated with mountains. As it connects us to the floor, we begin to feel more grounded physically and mentally.

How to do the pose:

• Stand with feet together or hips distance with the feet parallel to the mat.
• Have your heels in line with the second toes.
• Press down with all four corners of your feet and engaged your thighs.
• Lift your knee caps.
• Spin your inner thighs back and firm your hips.
• Release your buttocks towards the floor.
• Melt your shoulders down.
• Hold five breaths.

Enjoy!

Here is some more information on Tadasana  from Anne Asher, About.com Guide

Kinetic Chain
In tadasana, one stands upright against gravity in alignment. The feet are planted firmly on the floor. As the feet provide the foundation of the pose, even the smallest shift in their position will create posture changes further up the kinetic chain, affecting the legs, pelvis and back. Conversely, standing with a stable, balanced foot alignment will help you address imbalances of muscles that cause back pain. This is done when, in order to come into the pose, tight muscles stretch, and/or weak muscles work harder than usual.

There are three points on the bottom of each foot that should feel anchored into the floor: the mound of the big toe, the mound of the little toe and the center of the heel. (Mounds are located behind the toes themselves, and you can feel and see them as rounded masses.) Doing mountain pose with correct foot position and attention to the legs, arms and torso will begin to address postural and muscle strength .