According to Mendel's Law of Dominance in par of two contrasting characters one remain expressive while the other remains oppressive . The one which remains expressive is the dominant character while the other is the recessive character.It can be explained by Mendel's Monohybrid Cross.

The cross of the pod colours is given in the attachment below.

Hope i helped u:)
According to this law one character is dominant and other remains recessive . 
for eg  tallness of a plant is a dominant char but dwarfness is recessive and when two plants one tall one dwarf cross with each other the plant will ultimately be tall.