Where can I play online?

I used to play a lot with my friends when I was younger, but now they all moved on and I found myself without partners and time to find new ones.

Is there a good game or app to play online? I don't understand exactly how Magic: The Gathering - Duels of the Planeswalkers 2012 is different from the old magic online game... I was looking for something close to the real experience, that would allow me to build decks and duel people, etc...

How is the online scene?