How can I make my button work?

'if' and 'else' statements are wonderful things. It lets the program knows if a thing is in this condition, do these set of actions.

You can simply have your function laid out like this:

Boolean = true

function ExampleFunc()
	if Boolean == true then
		Boolean = false
	elseif Boolean == false then
		Boolean = true
	end
end

You can then shorthand the 'if'/'else' statement to save time and become more efficient (very important, and you will understand why).

if Boolean then
	Boolean = false
elseif not Boolean then
	Boolean = true
end

With not is equivalent to false or nil*. Consequently, the absence of not will make it true*.

*MISCONCEPTION: not actually means the opposite of a boolean value. Remember in math: if you multiply a negative number with another negative number, you will yield a positive number. So

not true == false

not false == true

Since the datatype we're manipulating is a boolean value, you can shorten the elseif statement into an else.

else
	Boolean = true
end

Because originally, the if statement says if the Boolean is true. Elsewise, it will be false.

To implement that knowledge into your script, you can have a static boolean variable and the set of ifs and elseifs.

On = false

-- Where your function starts

if On == false then
	On = true
	Workspace.Shadows1.Transparency = 0
	Workspace.shadowlight.PointLight.Enable = true -- You can preset your PointLight's brightness.
else
	On = false
	Workspace.Shadows1.Transparency = 1
	Workspace.shadowlight.PointLight.Enable = false
end