To defend against Kings Pawn Opening go to C5 the pawn covering your right bishop.
Continue to bring pawns down the right side until you can
A is to Castle.
B is to bring your bishop is open on the king or queen.
To win the queen your pawn must defend you when you attack or else it is a free bishop,
and devolpes the queen.
C is to eventually promote as he devolopes his castle, bishop, or a knight.
When attacking with king's pawn opening they are going to try the Sicilian Defense so you must move your knight to f3.
You can also move a pawn to d4.
You also can develop a knight or bishop.
Most people will to flank you on the right side to hopefully get a promotion and make your pawn a queen.
A good idea is to either out flank with a knight or open a rook and eat up the pawns if they are in a diagnol line like formation.
Credits to "WikiMedia Commons" and "Chess Klub"