The one of the goals of the TCGO seems to be to emulate the experience of playing the card game in real life, and the single player campaign takes you through a tournament hosted by a fictional game store, with 15 AI opponents (all with unique personalities and flavor text, including some good-natured trash talking), who you challenge through four leagues of 12 games each for a total of 48 games. The beauty of the TCGO is that it caters to all experience levels every step of the way, so even if you skip the tutorials, the single player has a help system that reminds you of your current play options and suggests optimal moves (of course, you can also turn all of help functions off if you don't need them).
If you're completely new to the Pokemon Trading Card Game, once you've logged in to your account (you can set one up here), you can go through the tutorial to learn the basics, or you can skip ahead to the single player campaign right away.
