Gui opens when player touches a brick?

This is an interesting question. It would be relatively simple to implement this incorrectly, but requires a bit of a process to do it the correct way. Since we want to comply with FilteringEnabled, the following method is the best.

First of all, create your GUI in StarterGui. Then, put a RemoteEvent in it, called "Show". On the same level, include a LocalScript. Your hierarchy structure should look like this:

• StarterGui
• • ScreenGui
• • • TextLabel (This is the GUI we will be showing)
• • • LocalScript
• • • Show (RemoteEvent)

Inside of your brick, insert a Script.

• Workspace
• • Part
• • • Script

RemoteEvents allow you to send data from the Server to the Client, and vice-versa. This is very useful when FilteringEnabled is enabled!

Inside the brick script, include the following:

script.Parent.Touched:connect(function(p)
	pcall(function() --We will use pcall here because something could very well go wrong, and we don't want our script to break
		if not p.Parent then return end
	
		local player = game.Players:playerFromCharacter(p.Parent)

		if not player then return end

		player.PlayerGui.ScreenGui.Show:FireClient()
	end)
end)

Now, what the above code will do is check whatever touches the part is a player, and if so, try to fire the RemoteEvent inside of the GUI.

Now, inside of the LocalScript (which is in the GUI), we will use this code:

local gui = script.Parent.TextLabel
local working
script.Parent.Show.OnClientEvent:connect(function()
	if working then return end -- We don't want to start fading if we're already fading
	working = true
	gui.Visible = true
	for i=1, 0, -0.1 do
		gui.BackgroundTransparency = i
		gui.TextTransparency = i
		wait(0.08)
	end
	wait(5)
	for i=0, 1, 0.1 do
		gui.BackgroundTransparency = i
		gui.TextTransparency = i
		wait(0.08)
	end
	gui.Visible = false
	working = nil
end)

When you put all of this together, you should get a button that properly fades in a GUI when a player touches the part.