How do you start off with breastfeeding ??

So I just recently learned that your milk ISNT automatically there when you give birth?? I might sound SO dumb but how come no one told me this?? 😂😭 how do you go about that? Do I tell the nurses I plan to breastfeed when I go in for labor?? Is the baby going to get enough milk if it’s not there????? IM SO CONFUSED? Are they going to give him formula? How do I know if the baby is even getting enough milk? ALSO what is the yellow stuff? Are they supposed to drink that & then it turns into milk or??

SORRY!!! It’s just I have no one to ask & I’m more on the shy side.. 😬 I didn’t know honestly anything & it seems like there’s more & more every time i think I got everything down? 😒