It makes me so happy to see someone who is 14 and already has this much enthusiasm for lettering. I especially like that he is using the no-slant style as I find that to be better for beginners. His style is more casual than what you would want if you want to learn a traditional italic.
There are many other videos on YouTube to look at before you decide which style you want to try first.
Lloyd Reynolds videos are a good example of more traditional italics.
Joan Fink has some nice videos using markers, if you want to give those a try.
Paul Antonio - good info, does not include full alphabet
and a person named John Neal, who is not the John Neal Bookseller,
has good tips for italic monoline penmanship
I'm sure there are lots more - so hopefully others will add to this thread.