The normal length of pregnancy in cats and dogs is about 60 days.
There are 3 stages of labor: nesting, active labor, and passing of placenta
Nature is an amazing thing and unless there are issues, the best thing you can do is leave mom and her babies alone - they are pretty good at taking care of things.
What Does It Look Like?
About 24 hours before active labor begins, the rectal temperature will drop below 100F
Once active labor begins, a puppy should be produced after no more than 30 min of pushing.
Once the newborn is produced, mom will chew them out of the membrane around them and chew the umbilical cord.
Between puppies/kittens, mom can take a break without pushing (up to 3 hours)
What Do You Do?
If at all possible, leave mom alone to do her job.
If a baby seems stuck, you can pull gently by the feet, but do not pull by the head
If mom doesn’t clean the puppies up afterwards, you will have to tear the membrane open and tie a small piece of string about ⅓ of an inch above the newborns belly and cut the cord above the string (placenta side)
Make sure to keep newborns warm and with mom if possible so they can nurse. Be careful with warming bottles or blankets that they are not too hot.
If mom pushes for more than 30 min without producing a newborn or takes longer than 3 hours between puppies, seek a veterinarian ASAP