Making a dragging placement tool?

I'm sure many of you have played the game Welcome To Bloxburg. In that game is an exmaple of a placement system that creates a start point of a wall and when the player drags the mouse, a preview of the wall is shown and letting go of the mouse button will place the wall.

I know how to make the first point but do not know how to make the preview wall when the player moves the mouse.

Any guidance/ideas on how to go about this?

PS I have looked into .magnitude and the Resize() function but am still stuck.