You just survive, not meaning to scare you as I have mum friends who's babies have only woken once or twice in the night from around five months of age, but I am having a terrible time sleeping and have only slept for more than four hours straight a total of 7 times in a year. The rest are between 45 mins-2 hours sleep.
I was someone who needed 9 hours a night plus a nap during the day. For the first two weeks my baby was born, I slept a total of 15 hours, the whole two weeks.
I'm now over a year in to motherhood and have been blessed with the best baby in the world but the worlds worst sleeper. On a good night she ll sleep 2-4 hours to begin with then up every 2-3.
On a bad night she ll sleep for two hours then up every 45 mins. One night recently she woke 17 times. However recently she has graciously given me a couple of nights where she's just woken once or twice so I know she can do it.
My advice, google 4th trimester, baby's sleep cycles, get proper swaddling sleeping bags, use a Moses basket so you can transport around the house, but a Rock-It automatic pram rocker so you can put baby in the bassinet of the pram in the lounge for a bit of a break whilst the rocking it rocks the pram for you, but most importantly be prepared to loose your sleep, it's natural.
Baby's want to be held, want to be close and want to feel secure. Remember they have been in you for nine months where it was warm, safe, cosy and had you're heart beat. Don't expect them to come out and just be able to be stuck in a cot and sleep. But then again you may strike it lucky and get a good sleeper ......