Plants need to undergo the two processes of pollination and fertilization prior to seed formation.  Just like humans have male and female parts, so do plant! The flower is the reproductive organ of the plant. Some flowers house both male and female reproductive cells/part. Other species of plants have male plant and female plants. In the discussion that follows, it will be helpful to look at the hyperlinked picture of a flower's anatomy. 

Pollen grains are the male reproductive cell of the plant. The ovule carries the egg. Pollination occurs when a pollen grain from an anther lands on the stigma. The pollen grain then releases an enzyme that enables it to travel down the style of the pistil via a pollen tube. Then the pollen grain penetrates the ovule and fertilizes the egg. The fertilized egg begins mitosis (cell division) to form an embryo. An embryo is a baby of the plant that is kept dormant in the seed until the right condition for germination comes.