Most cats are naturally good moms and instinct takes over, some are dumber than dirt and will let their babies die...but this is rare, thankfully.

If they are normal, they'll usually be OK and not need any help from you. But if you get a dumbass, be prepared to possibly have to pull the birth sac off and trim the cord. Leave it very long, it will dry up and fall off later on.

Watch that she doesn't freak and take off running mid-birth - close any escape routes ahead of time. I've delivered dozens of litters, usually goes fine.