They find the best candidate male they can, and the best candidate female.
Most breeders do controlled pollination though; they don't just let the males explode all over everywhere.
Typically, the candidate male is separated from the females, and the pollen is collected and saved in a controlled manner, before the pods open up on their own. Once the candidate females are at the right stage of flowering, the pollen is 'painted' on to the specific bud sites of the female that they want to produce seed, and then carefully, the females are placed back into flowering with the other girls.
To produce feminized seeds, you can't use a male plant. What you do is force a female to produce pollen. The most reliable method is spraying a 40-50 PPM colloidal silver spray on the bud sites of a female right after she goes into 12/12. This is done once or twice a day for a few weeks. She's usually separated from the rest of the flowering plants. Then, just like above, the pollen is collected and saved. Then, typically, the rest of the process is carried out the same as above. The pollen is painted (with a fine painter's brush, or q-tip) onto a different flowering female plant that will then produce the fem seeds. They are fem because it is literally a female plant pollinating another female plant.
Allowing a male to just spew pollen everywhere in a grow is very messy, and a pain in the ass to ensure the cleanup is done correctly.
-spek
ps. I'm just starting my first colloidal silver breeding/seeding process this weekend. I clone a bunch of plants, but my main reason is to collect fem seeds to preserve my strains long term, and to test my hand at cross-breeding two separate strains. Clones are great, but if your crop gets wiped out, seeds in the fridge make sure you can get going again.