Some plants are wind-pollenated. That’s true of most conifers, and it’s also true of many grasses. Such plants are highly evolved; they depend on nobody and nothing for their reproductive functions. Unfortunately, such plants also cause bad reactions for allergy sufferers, because they release all that pollen into the air.
Other plants are cross-pollenated by, well, birds and bees (and other insects). Critters unknowingly collect pollen from the anthers of one plant and move along, to deposit the pollen into a stigma.
So, the “birds and the bees” explains the mechanics of sexual intercourse.
“Birds do it, bees do it
Even educated fleas do it
Let’s do it, let’s fall in love”