delivery of the placenta?

So i’m in grade 12 and we are currently learning about human reproduction, one of the sub-sections is about the delivery of the placenta or after birth.

I’m just curious.. does the placenta have to be pushed out after the baby is born or does the mom just have to wait awhile and it’ll pass out the vagina on its own? and is it just a mucus type of thing that’s discharged ?

thanks !