How do I make a Gui show up for certain people?

-- A simple one for non-experienced coders. Put this in a "LocalScript" and put it inside the Gui. Change the names in "Admins" to who you want to be able to use it and leave the Gui in StarterGui.

local Admins = {
    "darkelementallord",
    "ThatGuy",
    "Meh"
}

local Allowed = false

for _,n in pairs(Admins) do
    if (n:lower() == game.Players.LocalPlayer.Name:lower()) then
        Allowed = true
        break
    end
end

if (not Allowed) then
    script.Parent:Destroy()
end

To make a gui show up for certain people, you must insert it into their PlayerGui. The PlayerGui object is a container that holds a Player's user GUI. So, we want to insert the gui we are making, into the playergui of the player that we want to have the gui onscreen.