Start with the Breath
Even if you've never done a single yoga pose, you've been practicing an important element of yoga since you were born: breathing. The entire physical practice of yoga is built on the premise that if you can learn to train your breath to be even, no matter what type of posture you're doing, you can also learn how to train your mind, body and spirit to remain grounded and open no matter what life brings. It doesn't matter what kinds of interesting shapes you may be able to make with your body; if you're not breathing while you're doing it, it ain't yoga.
To get started, sit quietly in a comfortable cross-legged position. Sit on the floor with a pillow under your sitting bones so that your hips can be higher than your knees. Lengthen the spine so that your ribs are lifting away from your pelvis. You can keep your eyes open or let them close. Then spend a few minutes listening to your breath. That may sound simple, but you'll soon figure out that it's not. Your mind will want to wander. Just bring it back to focus on your breath as many times as you need to. Notice how it feels to breathe—where do you feel the breath in your body? How does that change if you make your inhales and exhales a little longer? A little shorter?
Throughout the day, periodically check in with your breath. What is your breath like when you're resting, eating lunch or having a tense conversation with a loved one? How often do you find yourself holding your breath? Become extremely curious about the way you breathe. You don't need to change your breath at all, just notice what your patterns are.