How to attach a part to another in game?

First, I'm kinda new to scripting and I have this idea that I wanna use in my game. I want to be able to attach an equipped part on to another part I previously placed down.

So, I have a (squared part) in my character's hand that I'd want to place on the edge of another (squarepart) I previously placed down on the baseplate. I wanna make it so once I equip the part, four green place holders will appear on the edges of the (squarepart) that is on the baseplate. And so, while having the part equipped, I would use Ray Cast/Pointer to click on any green place holder I wanted to place the equipped part in. After left clicking on the place holder, the equipped part will automatically be placed on the edge of the squarepart that is on the baseplate. Any advice on how I can do this?