Flowers are the tools that plants use to make their seeds. The basic parts of the flower are shown in the diagram below.
Seeds can only be produced when pollen is transferred between flowers of the same species. A species is defined a population of individuals capable of interbreeding freely with one another but because of geographic, reproductive, or other barriers, they do not interbreed with members of other species...
How does pollen get from one flower to another? Flowers must rely on vectors to move pollen. These vectors can include wind, water, birds, insects, butterflies, bats, and other animals that visit flowers. We call animals or insects that transfer pollen from plant to plant “pollinators”." From the US Forest Service
JGL note: pollination is far too complex a process to have developed by evolution.