Giuoco Piano and Evans Gambit

http://www.chess.com/article/view/the-evans-gambit-by-gm-magesh-and-gm-arun

this might help.

http://www.wesdel.com/FarragutCC/Lessons/EvansGambit01a.pdf

and this.

i always loved playing the evan's gambit.

The Evans is pretty sharp for black. Thx for the links

Question 1: When you look at the diagram position you can see that black can play d5! the counter strike in the center works because the white bishop is placed on c4. After the forced exchange on d5 the position is completly equal and white has no realistic winning chances. Note that playing 7. Nc3 is possible this is a dangerous pawn sacrafice that however with good defence is better for black. This is actually the reason why many strong players prefer the Ruy Lopez over the Italian game. In the Ruy Lopez the white bishop often ends up on b3 (after 3 .. a4 4. Ba4 etc). The bishop is actually placed better on b3 than on c4 because than the counter strike d5 is not possible. 

To answer your second question. For 1 pawn compensation white got a a firm grip on the center, superior development and he can castle quicly. For black castling is harder because on Nf6 moves like e5 with even more space and open lines follow. In other words in the evans gambit generally black has compensation for the pawn because of center combined with open lines