Yeah backing a result is like saying it will happen like you normally would. If you lay a bet you're basically saying it won't happen.
Eg United vs QPR
Back United would mean you'd get paid if United win
Lay United would mean you'd get paid if its a draw or QPR win
Ok, so that makes sense now but this makes the 'back' bet matched, what's the difference between a matched bet and an unmatched bet?