I'm going to assume you already have a gui with some type of a gui button.

So, inside of a local script inside of your button you want to use the MouseButton1Down event.

script.Parent.MouseButton1Down:connect(function()
    -- Teleport the player
end)

Inside of that event, we want to make sure the player's character exists.

    if game.Players.LocalPlayer.Character then
        -- Commense the teleport!
    end

After that, just generate 3 random numbers, with math.random, and use the MoveTo method on the character to move it to that location.

        local x = math.random(-10, 10)
        local y = math.random(-10, 10)
        local z = math.random(-10, 10)
        game.Players.LocalPlayer.Character:MoveTo(Vector3.new(x, y, z))

Well you could just use this instead, although you'd have to adjust it to make you teleport randomly.

function Click()
script.Parent.Parent.Parent.Parent.Character.Torso.CFrame = CFrame.new(#,#,#)
end

script.Parent.MouseButton1Down:connect(Click)