Squash plants are monoecious (moun-e-she-us), which means they have male flowers and female flowers on the same plant. However, if pollen does not get from one to the other, pollination and fertilization do not occur and the potential fruit aborts. The pollen is usually moved by insects (bees, flies, etc.). If there is insufficient insect activity, which is often the case in a home garden, you will not get any edible squash or, if partially pollinated, the squash will be odd shaped.
If you have little or no insect activity in your yard, you will have to pollinate the female flowers. In the morning, carefully pick an open male flower with its stem and remove the corolla (petals), then using it like a Q-tip dust its pollen onto a female flower. Usually one male flower will provide enough pollen for one female flower. Once you get good at it, one male flower may be used on two or more female flowers.