Instinct and common sense are powerful helpers. I'd never even held a baby before I had my DS. DH showed me how to change a nappy and dress him (he has a niece and nephew) then left me to it on that first, memorable night on the post natal ward. I was terrified but did actually cope!
If neither of you have a clue and neither of your parents will come and show you, you need to ask the midwives at the hospital. They will show you how to dress/undress/put a nappy on etc. They won't if you don't ask though. Read and read and read on the internet, watch videos etc. Buy one of those books that take you through the first few weeks (for reassurance really!).
For practical help, rope in friends who have children already, and family. If you have none of those, there is NHS help. When baby is born, they will show you the basics if you ask. Then as soon as you're home there is a visit on day 1 to check you're ok (and to offer advice if needed). You go back to the hospital on day 5 and again at day 10 to check weight etc and can ask more questions if needed at this point. Then there's the first Health Visitor visit between 10 days and 14 days. After that, you'll know where and when the Health Visitor clinics are and can go at any time to have baby weighed and ask advice. So don't panic, even if you have no one you know to help/advise you, the NHS has it covered!
It's great - so great that lots and lots of people do it more than once. Life changing in a very good way, and so very worth nine months of being pregnant. Hard work though!