What have you looked at to learn the long tail cast on? There is a video of it on this site, but I think it is not the easiest way to learn to do it. I always teach it beginning with a slip knot and then cast on and I do it with 2 hands instead of one (but one handed is not that hard, I just prefer 2 hands). Here is a link to a video showing the way I do it. Give it a try. LINK
I don't believe the gal shows how to do the slip knot to get started but starts after that is done. If you need help with that I suppose you could do a search for "how slip knot". You want a slip know tied over a needle or hook.