How do i fix this Open and close GUI script?

well, you could write the code in fewer lines. liek this:

local morphs = game.Players.LocalPlayer.PlayerGui.Catalog.Morphs
script.Parent.MouseButton1Click:Connect(function()
    morphs.Visible = not Visible
end)

btw, there must be some other parts in ur code thats making it not work..

one of which could be that an error is taking place, because u forgot the if keyword or game.Players.LocalPlayer.PlayerGui.Catalog.Morphs is not a true directory, and etc

Well you did one simple mistake. Here's the corrected form:

script.Parent.MouseButton1Click:Connect(function()
    if game.Players.LocalPlayer.PlayerGui.Catalog.Morphs.Visible == true then
        game.Players.LocalPlayer.PlayerGUI.Catalog.Morphs.Visible = false
    elseif game.Player.LocalPlayer.PlayerGUI.Catalog.Morphs.Visible == false then
        game.Player.LocalPlayer.PlayerGUI.Catalog.Morphs.Visible = true
    end
end)

Basically you just missed putting an "if" before the first statement. Here's a shortened version of your code if you'd like to use that:

local Catalog = game.Players.LocalPlayer.PlayerGui.Catalog

script.Parent.MouseButton1Click:Connect(function()
    if Catalog.Morphs.Visible == true then
        Catalog.Morphs.Visible = false
    elseif MorphCLog.Visible == false then
        Catalog.Morphs.Visible = true
    end
end)

In the shortened version, a variable was added for your morph catalog and when you use it, you can use the variable instead of the long version.

Hope this fixed your problem. :)

Edit: Sorry if it might not be indented perfectly. Just re-indent (recommended) them correctly or un-indent them.