[ Oh well that is easy enough! And something Anders rather enjoys talking about. ]

Let's see...there's this place called the Fade. It's where everyone goes when they dream - though the Fade in this world seems....different somehow - but only mages can remain conscious within it. It's this connection that gives us our abilities, as magic is channeled energy from the Fade. This link is something we are born with - it can't be learned and it can't be unlearned, which is somewhat problematic when the connection solidifies in early adolescence and we start burning down barns whenever we feel angry. [ He's smirking, but there's a hint of something harder, resentment or pain or just general uncomfortable feelings. ]

There's a great deal more to it than that, but I think I've covered the basics - Fade connection, teenage emotions, and bam; sparklefingers. [ Anders wiggles his fingers dramatically in demonstration. ]