After Effects stroke effect doesn't play
It looks like you're changing both the Start and End of the Stroke effect. If you want the text to write on completely, you need to use just one or the other. Which one you use will determine the direction the Stroke is animated in.

The effect will have to be activated and set to "Reveal Original Image" in order to see the animation demonstrated in the YouTube video (which, by the way, is a horrible masking example. I recommend watching some tutorials on using the Pen tool in order to create better masks).