Noddy is correct. Male flowers are on a long stalk, female flowers are at the end of the young fruit. You can pollenate them yourself by taking a male flower, removing most of the outer membrane to expose the anther, and then sticking it inside the female flower.
You can also do this with your finger, but watch out for bees. If there are bees around, you probably won't need to do this, but I've had success with all types of squash.