How do I Make a Starter Screen GUI?

You could use this to fade in a text label in a gui:

for i = 1, 0, -1 / 30 do -- -1 / 30 is used to make the transparency go down to 0 in 1 second.
    someTextLabel.BackgroundTransparency = i
    wait()
end

To make a gui appear on the screen when you join, just stick a ScreenGui into game.StarterGui, and put things such as frames and text labels into the screen gui.

Gui creating can get tricky at times when you are trying to alter the exact size, but as far as scripting wise when you want to fade something, use a for statement.