so I modeled a body and a hand separately after this I used the hand and aligned it close to the wrist , I Check auto merge option than snapping tool - vertex - and when I try to merge vertices merge my hand to the wrist but it goes they are merging at the center of the body , I m pretty sure its about the mirror modifier or something , I just need a quick help please , thanks in advance guys here is some pictures
You have selected vertices on both sides of the body, and are merging them At Center. The average position between all the selected vertices is in the middle of the body, so they all merge there. I think you meant to use Merge By Distance.
On a second note, this would still be redundant to Auto-Merge and thus unnecessary, or rather ineffective. Because the cutoff of the wrist does not precisely match the cutoff of the arm, I might use Bridge Edge Loops instead, one arm-wrist pair at a time. Merge Vertices is not the interpolating tool you seem to think it to be, but Bridge Edge Loops is closer to that.
On a third note, it appears that this mesh is already symmetrical in real geometry, so the mirror modifier is also redundant. I recommend you delete it lest it cause confusion or Z fighting later.
