How do you point an arm towards the mouse? [closed]

I'm making a paintball game, and when I played it with my friend, he suggested to make it an FPS. So, I tried to make an FPS mode, but I'm having trouble with one thing: how do you make your arm point towards the mouse? I looked in the Urist's pistol model, but I don't get it. What is a simple way to make the right arm point towards the mouse?

When I tried it, the arm pointed in the wrong direction. I used this code:

tool.Equipped:Connect(function(mouse)
    local char = tool.Parent
    local joint = char.Torso['Right Shoulder']
    while tool.Parent == char do
        wait()
        joint.C0 = CFrame.new(joint.C0.p, mouse.hit.p)
    end
end)

I tried copying the code from the pistol model. It did work, but at one point it deleted my character,