When aircraft pull too much angle of attack, the wing abruptly suffers a loss of lift anywhere the maximum lift coefficient has been exceeded. If your entire wing loses lift all at once this can be very dangerous. As a result, most wings are designed with what's called Washout, wherein the angle of incidence at the root is greater than at the tip. This causes the wing root to stall before the tip, which allows a pilot to maintain control as the onset of stall appears.

Using a forward-swept wing causes the spanwise (along the wing's length) flow to be net inward, rather than outward which is the case in a conventional aircraft. With the right mix of composite materials to control aeroelastic twist this causes a similar effect to washout wherein the wing root will stall before the tips, but greatly reduces wingtip vortices and thus reduces total aerodynamic drag. As someone else pointed out, you also get an induced drag benefit because both the canards and main wings are producing upward moments, so the total magnitude of lift force required for a given weight is less.

The "so what?" of all that is it lets you build a smaller, faster, more agile aircraft at the cost of significantly increased aerodynamic and control complexity.