Learning to play poker online really isn't all that different from playing poker at a card room. The only major differences are how you deposit, and how much rake is taken from each hand that is played.
Depositing into an online poker room has become a little more difficult recently. For one reason or another the United States has tried its hardest to keep the American poker player from being able to play cards online. Probably the best way to play poker online now is through full tilt poker. Through full tilt poker you can deposit directly to your poker account from your checking account.
The rake at full tilt compared to at a live poker room is one of the greatest benefits to playing poker. The rake at a live poker room can be up to 10%. At full tilt poker this number is far smaller. On average you will be looking at more like 3-7%. This means more money in the pockets of the winning players.
Another great benefit to playing online versus a live card room is that online almost all of the poker sites will give you a deposit bonus. Full tilt will give you a 100% matched bonus of up to $600. This bonus is not given to you all at once, you just need to play through a certain amount of hands and the bonus will be released to you. Some poker players will jump from poker site to poker site just clearing their bonuses and make some pretty decent money that way.
Don't be intimidated by playing online. It is really not that different from playing live it can just take a bit to get used to.