Well one of the first scales you should learn, if not the first, is the major scale. A few others are the minor pentatonic and natural minor scales.

G major Gm Pent. G natural minor
e |---------5----7---8---|--3------6--|-----3----5--6--|
b |---------5----7---8---|--3------6--|-----3-4-----6--|
g |-----4---5----7-------|--3---5-----|--2--3----5-----|
d |-----4---5----7-------|--3---5-----|-----3----5-----|
a |--3------5----7-------|--3---5-----|-----3----5--6--|
e |--3------5----7-------|--3------6--|-----3----5--6--|