Fianchetto
Developing a bishop on the long diagonal, from b2, g2, b7 or g7, after moving the knight's pawn.
The bishop on g2 controls the long diagonal from h1 to a8, and shelters the castled king. The cost: the pawn move leaves small weaknesses around it.
New to chess? The examples here use it. Play your first moves (five minutes), then learn chess from the beginning, one short lesson at a time.