The male and female flowers themselves look about the same, but the females form at the end of a baby squash, and the males form at the end of a plain thin "stem". If there are no bees buzzing around your flowers, take a little paintbrush and get some pollen from the male flowers and daub it into the female flowers.

Another tip to ensure pollination by bees is to plant some of their favorite flowers (like cosmos) near your squash.

Hi Alamo5000, what happened to your zucchini last year?

Here's what a female blossom will look like, even before it opens:

{{gwi:59327}}

The male won't have the thickness at the end, and you'll be able to clearly tell that it's just growing from a plain 'ol stem.