Holding the violin, for a beginner, is one of the most important things to learn when you are first learning how to play. I feel it is one of the mistakes that is made sometimes where children learn to hold the violin with their hand. Really they should be learning how to hold the violin with their chin only. Here is a demonstration of what should be happening when you learn to hold your violin.
First of all, you start in rest position. Again, this is for a young, a beginner. Your feet are together. You make a V for violin. Then you step out with either foot, it doesn't matter which one so that your equal distance apart from your shoulders. Your shoulders should be the same, parallel to your shoulders should be your feet. Then, you take the shoulder of the left side of your violin with your left hand and you put it out in front of your left foot. Your arm should be nice and straight. Then you turn the violin over so it's upside down and you fly it into your neck.
Now, this part is the most difficult part because you want to make sure that you can't really see the top of your shoulder. A lot of the mistakes are made when the violin is held like this and you can see the whole shoulder. Then your not really holding the violin well enough. If it is on top of the shoulder you should be able to let go and even put your left hand on your right shoulder.
Your head position, your head should be turned but also relaxed and a little laid backward like your sleeping. Not too much but a little bit. You're staring at the D string and your using about half of your chin and half of your cheek to hold the violin. Half of your chin, not the whole thing 'cause that's what that would look like, and half of your cheek right over here. This is the right way to hold the violin.
You could walk around your house demonstrating how well you hold your violin. Shake somebody's hand. Have a destination to where you are going and practice this. This is how you need to do it in order to keep your fingers. Letting them free. Keeping them free so they can shift all over the violin instead of having to hold them. Hold the violin. Then they won't be able to shift as freely.
This is a beautiful violin position. Again, feet together. Make a V, step. Left hand to left shoulder. A straight arm over the left foot. Flip it over, fly it in. Make sure it is on the shoulder using half your chin, half your cheek. Left hand flies to the right shoulder. And you have a beautiful violin position. The violin is also nice and flat. And that's the right way to hold the violin.