Just confirming what others have said, really.
If the baby cries, offer it food. If that doesn't work - nappy check, try to bring up a burp, try to see if the baby will sleep. You'll get to know the signs for some of these things fairly quickly.
It's almost always hunger with my 9 week old - and it's been that way since she was born. Sometimes she cries when she gets over-tired.
The baby might be hungry very often - even if it's just fed 10 mins before and then starts to cry again, it could be hunger again. Remember how tiny their stomachs are and how fast they empty!
Get into a routine, whatever suits you and the baby best. Our routine is that she feeds one side, then has a nappy change, then feeds the other side, and then either sleeps, or plays for a bit and then sleeps.
I was totally clueless too - 9 weeks in, and I feel like I've known how to look after babies all my life. And it's felt like that since perhaps a week after she was born.
Good luck! And remember, she will never remember your first few botched attempts at putting on a nappy, or a vest! Just go with the flow and try your best to keep her full, clean and warm