If your dog is pregnant you probably will not notice anything for the first couple of weeks. In the weeks that follow you should notice an enlargement of the nipples along with an increase in their appetite. About four to five weeks into a pregnancy you should notice a clear vaginal discharge and at this time if you take your dog to the vet they will be able to pick up fetal heartbeats on an ultrasound.
While your dog is pregnant make sure they still get a fair amount of exercise in order to stay healthy. If you are not already feeding her a premium brand dog food, now is the time to start. Pregnancies in dogs last right around two months. When you feel it is getting time for your dog to deliver her puppies, spend some time with her so you can help out if she has any difficulties in the delivery process. If you like, many vets are more than willing to help a dog deliver her puppies.
Once your dog has delivered her puppies make sure she has plenty to eat and give her some milk to aid her in the process of making milk for her new puppies.