For example, on Spectrum nightclub some of the blocks have bright outlines
Really simple. It should be placed inside a PlayerGui but doesn't have to be. If it is placed in a PlayerGui it is local so only the player can see it.
selection = Instance.new("SelectionBox") selection.Parent = script.Parent selection.Adornee = script.Parent
The Adornee property is very important. It is the part that the selection box surrounds itself around.