I've just bought the game and I'm a bit confused what the completion of challenges gives me apart from bragging rights, and what the symbol and number listed to the right of the challenge description refers to. I guess it's some kind of scoring mechanic, but what does a score value get me, and what do the symbols mean. They look like they are refering to defense(shield) accuracy(target) etc but does that mean that those stats improve or are they just simply a means of identifying challenge category?

Any information would be greatly appreciated.