How to use a GUI for a decal insert-mabober?

I am at a loss here. The goal of this script is when the "insert button" is clicked then the number string in the textbox will be the preexisting decal id. Here is my script

button = script.Parent
DecalId = script.Parent.DecalId
screen1 = game.Workspace.screen1
screen2 = game.Workspace.screen2

function onclicked()
    screen1 = "http://www.roblox.com/asset/?id="..(tostring(button.idInput.Text - 1))
    screen2 = "http://www.roblox.com/asset/?id="..(tostring(button.idInput.Text - 1))
end

script.Parent.idInput.MouseButton1Down:connect(onclicked)