You love ballet, or you would be reading a different article. I get it!
So, whether you've been studying ballet for years, or you are just thinking about taking ballet lessons, you are curious - how does my present posture affect what happens in ballet class?
And how does how my feet rest on a floor affect getting good basic ballet positions?
So let's start before first position. Excellent posture is: your heel bone and ankle bones above, are vertical - 90 degrees perpendicular to the floor. All your bones, knees, hips, spine (with natural curves), neck (another natural curve) stack in a straight line above. In your imagination, like Superman, you can see this with x-ray vision.
So when your ballet teacher shows how you turn out, rotating the thigh muscles with the knees and feet following to turn out to the same degree, your excellent posture does not change in any way. Your ankles, knees, hips, spine, neck and head are still stacked up in a straight line.
When you learn to point your working foot and lower into second position, nothing changes except for how far apart your feet are.
At third position, depending on your natural degree of turnout, and the width of your pelvis, you may be able to have one foot closed at the arch of the other foot, without feeling a tug or strain in the hip area. If the hip over the front foot moves forward, stretching may eventually dissipate this, or maybe not. Ballet turnout is a whole other subject.
Fourth and fifth position have the same challenge of third, which is, getting the feet right and ideally having the hips in line sideways, not angled under your waist.
All these details can help, even if you never reach the ideal. If you are an adult ballet beginner, this is tougher, but you can improve. You can get good basic ballet positions, and prevent dance injuries.