This is Gregor Mendel, a scientist who discovered the fundamental laws of inheritance.
Here are two butterflies- there are two different alleles, either pink or orange. The pink one is dominant the orange one is recessive. For these homozygous butterflies, the genotypes are PP (the pink one), and pp (the orange one).
When the two homozygous butterflies have babies, the dominant gene, (pink) is transferred to the children. This means that all of the children (F1) of the two different butterflies will be pink, but they will be heterozygous because they inherited one pink gene and one orange gene.
When the two new heterozygous butterflies have babies, each of them transfers one gene to the children, either pink or orange. The F2 babies could either be pink or orange, depending on what gene the parent butterflies transfer. They will most likely be pink, but have a 25% chance of being orange.