Which components I need for creating a dragger like Studio selection tool?

So, I'm trying to create a dragger like the Roblox Studio selection tool but most scripts that I have made are based on the mouse normal so I can't really make the CFrame relative to the target part CFrame, I was looking for keeping the rotation from my CFrame but making it relative to the target part(This is where I don't know how to start and I would like help with it)

Here's a visual example of what I want to achieve

I was trying to implement the maths from this post https://scriptinghelpers.org/blog/creating-a-furniture-placement-system because it seems to have what I want but I barely understand it