How does tool welding work?

I am starting to get the basics but I still don't understand how people create functions for weapons such as crouch and crawl. I realize some people copy these functions but I would like to do it myself so it is more original and I can understand it. At the moment I am trying to simply weld the arms when the tool is selected so that both arms are gripping the tool, not just one. I have tried looking at complex scripts but its a bit confusing to me since I haven't really learned things like sine and cosine yet, I've only learned Algebra 1 stuff so far. If someone could help me that would be great! If this is off-topic please let me know where I should be requesting for help!

Ok first, You insert a Tool into the workspace (Name the Tool, what it is, Example "Sword") Insert a Part into the tool and name it "Handle" Then insert a Weld into the Tool If you've coded it put the script inside the Handle. Drag the tool into the starter pack and insert this script into the Tool:

function Weld(x,y)
	local W = Instance.new("Weld")
	W.Part0 = x
	W.Part1 = y
	local CJ = CFrame.new(x.Position)
	local C0 = x.CFrame:inverse()*CJ
	local C1 = y.CFrame:inverse()*CJ
	W.C0 = C0
	W.C1 = C1
	W.Parent = x
end

function Get(A)
	if A.className == "Part" then
		Weld(script.Parent.Handle, A)
		A.Anchored = false
	else
		local C = A:GetChildren()
		for i=1, #C do
		Get(C[i])
		end
	end
end

function Finale()
	Get(script.Parent)
end

script.Parent.Equipped:connect(Finale)
script.Parent.Unequipped:connect(Finale)
Finale()