Script to weld a part to arm?(Please help)

I want a script that when in build mode then I enable the script a part is welding to my arm so it has a part and the arm fused kind of look?

This is not a request site. I'll give one hint. Only one chunk i'll give

game.Players.PlayerAdded:connect(function(plr)
plr.CharacterAdded:connect(function(char)
local cloned = script:Clone()
cloned.Parent = char.Right Arm