The bitch will began to bleed. The first 1-8 days not much changes until she goes into standing heat at about day 9. ( breeds vary ) 

Standing heat means she will be receptive to the males advances. She may lift her tail, dance in front of the males face. A test is to run your hand down her back, if she is in standing heat, she may lift her tail. 

A good stud will not attempt matting until the correct time which is when she is ovulating. He senses this by the smell of progesterone that she will give off during ovulation . Breeding will take place on days 10, 12,14. for Smaller breds, Larger breds may ovulate earlier. If you are unsure of her best days to bred her, than take your female to your Vet for a vaginal cytology or contact Camelot Farms, they have a new Ovulation test on the market called Premate. 

When the female ovulates, it take 48 hours for her eggs to ripen before they will allow penetration of sperm. 

She may release 200 eggs which the male may fertilize. Her body and mother nature will absorb the unhealthy and some healthy fertilized eggs. Leaving fertilized eggs that her body is capable of carring to term. There are occations when mother nature brain drives off the map and she absorbs them all. This is usually about the time you go yelling at the stud owner, saying her dog is no good. It is not always the studs fault that your female did not go on to whelp a litter of pups. There are a number of reasons a Female will fail to concieve. 

Age - to young or to old
Irregular heat cycles- it may not be a true heat
Bred on the wrong days - this is why ovulation testing is important. You may of bred to early or to late.
Stud has low sperm count- Always use a proven male, one that has sired other litters.