Setup and Key Actions of Bound Angle Pose
Sit tall. Bend your knees and bring the soles of your feet together. Press your fingertips into the floor beside you to activate your low belly and lengthen up through the crown of your head. Spread your toes to activate the muscles of your legs, and internally rotate your thighs to help maintain a natural curve in your lower back. If you need to adjust the distance between your feet and your hips, move your hips toward or away from your feet instead of moving your feet toward or away from your hips, which can twist the knees.
If your big toes feel "stuck" together (i.e., you can't separate the big-toe sides of your feet without also separating the pinky-toe sides of your feet), your knees will be happiest if you avoid folding forward and remain upright in the pose. If you're able to keep the pinky-toe sides of your feet together and open your feet like a book, then you can fold forward if you wish. Don't worry about bringing your face to your feet. Instead, focus on maintaining length through your spine and make sure that your spine is rounding evenly throughout (as opposed to, for example, rounding primarily in your upper back). If not, back off the forward bend and focus on finding length in your spine.
Modifications of Bound Angle Pose
If you find that you're rounding your lower back and are unable to sit up straight, sit on a folded blanket or place a block underneath your feet. You may also find that elevating your feet allows you to find more opening in your hips without straining your knees.