Editing shape after parenting armatures After parenting the body with bones I tried to modify the shape and add more loop cuts in edit mode but, when I am trying to move the hand in pose mode I got this shape? so, what is the issue?
Your weight paints are probably off. Click on your model, switch to weight paint mode, go to Object data properties panel, and click on the bone causing the problem under vertex groups. Where the problem is occurring, there should be red dots. Change the brush type to subtract and make the color of the red spots causing the problem blue.
Here is where you click on your bone:

Click on the option that has the name of the bone causing the problem.
If you want me to elaborate, just ask.