I always have a whelping kit ready(not that I breed many) This consists of peices of old towelling to hold a pup's head (DO NOT PULL, JUST HOLD!!!!!) to stop it being drawn back in, sterilised butcher's string (if need be make two ties between pup and bitch and cut as Doganjo said with blunt scissors or you can use your thumb and first finger nails in a sideways "chewing" action.Use anti bac. gel on your hands though. A heat pad or well wrapped hot water bottle may come in useful as will a roll of kitchen towel.
The best thing you can do is to keep calm, be near the bitch but don't fuss over her and let nature take charge. She will probably do it all by herself.
I do hope all goes well, I'm sure it will. P.S. to sterilise string put it in a kilner jar or similar and put into a hot oven for 5 minutes or so.