Why doesn't my Grow/Shrink Script work?

function grow()
    script.Parent.Size=script.Parent.Size+Vector3.new(1,1,1)
end


function shrink()
    script.Parent.Size=script.Parent.Size-Vector3.new(1,1,1)
end

script.Parent.ClickDetector.MouseClick:connect(grow)

script.Parent.ClickDetector.MouseClick:connect(shrink) -- You'll need another way of shrinking because you cannot use right click unless you use mouse and get target and check it then

Here's how it would work with a localscript and using the players mouse:

local Player = game.Players.LocalPlayer
local Mouse = Player:GetMouse()

local Part = workspace.Brick -- your part's directory

function grow()
    Part.Size=Part.Size+Vector3.new(1,1,1)
end


function shrink()
    Part.Size=Part.Size-Vector3.new(1,1,1)
end

Mouse.Button1Down:connect(function() -- if the player left clicks
    if Mouse.Target == Part then -- checks if the mouse is over the part when clicking
        grow()
    end
end)

Mouse.Button2Down:connect(function() -- if player right clicks
    if Mouse.Target == Part then  -- checks if the mouse is over the part when clicking
        shrink()
    end
end)

Hope this helps

ClickDetector doesn't have Button1Down or Button2Down events. It only have MouseClick, which can be activated by Left and Right mouse buttons. It can't detect only right or only left mouse clicks, so your script can't work. But you can find another ways.

Anyway, grow or shrink function still can work, if you change Button#Down to MouseClick.