How do I do a typing like affect on text labels?

Continuously add characters to the TextLabel.Text property. In this example I've bound the typing text effect to a BindableEvent. You can change this if you like.

local final = "Hello World!"
local label = script.Parent
local event = Instance.new("BindableEvent") -- don't set the parent yet
event.Name = "TypeLabel"
event.Event:Connect(function ()
    label.Text = ""
    for i = 1, string.len(label.Text) do
        wait(0.1)
        label.Text = label.Text .. string.sub(final, i, i)
    end
end)
event.Parent = label