How do I make a UI visible for everyone in the server?

Hey.. I'd like to know how to make a UI visible for EVERYONE in the server. I did it a few times. But I literally did something with remote events, I don't know how I did it. Thanks!

To make a GUI Visible for all players, you can use 'FireAllClients', just like JesseSong said.

Server Sided Script:

local Event = EventPath:WaitForChild("EventNameHere") -- RemoteEvent

-- Do whatever
Event:FireAllClients() -- Fire this to every player.

Local Script (In the GUI Object):

local Event = EventPath:WaitForChild("EventNameHere")

Event.OnClientEvent:Connect(function()
	script.Parent.Visible = not (script.parent.Visible) -- Toggle it on or off, depending on its current state.
end)

You can use a remote event with :FireAllClients like JesseSong and oilkas stated. If you don't know how to use RemoteEvents, I suggest checking this page: Remote Functions and Events