Because they are in computers, each person could have a 'port' or 'chipset' or something where they can add or remove programs to change abilities. They could give eachother viruses, you could actually go a long way with that idea. You could treat different servers like different worlds, I dunno, you could go far with this idea.
As for starting it out, I see a stadium full of holo-screens instead of seats. Tens of Thousands of viewers remotely view and gamble on a fight that's taking place between two users. Wealthier viewers purchase the better, bigger and closer monitors, and the kingpin of the casino is displayed on a floating monitor over the stadium, announcing the fight and urging viewers to place their bets.
Maybe your main character isn't actually in this battle, but since you said he's poor, he's actually watching the fight from the stadium in person. He's trying to to be seen, as no one actually attends the stadium to watch the fight inside, they simply purchase the monitors. There are still guards, however, so he must be discreet. His dream is to become a Gladiator or whatever, I realize Gladiator is cheezy, but I mean his dream is to become a wealthy and noteworthy combatant, so that someday he can escape through The Network.
He is spotted by a guard, who releases a low level Security Program, which takes the shape of a vicious dog and chases him out of the stadium.
Maybe you could use a lot of computing and programming terms to sort of relate this world to our understanding of computing. For example, someone could have an ability to guard against virus attacks by creating a 'sandbox' around them. Not actual sand, but a field of energy, you know what I mean.
And perhaps people learn to be hackers to earn their freedom, like you said, and one would do so by hacking their way out of the heavily encrypted network that leads to whatever or wherever your ultimate roads' end.
Sir, you have a good idea, I didn't mean to hijack it or try to over-suggest stuff, it's just when I hear a good idea, my imagination starts to flare.