Help Explaining Xenomorphs and the Black Goo

1. How is the goo connected to xenomorphs in means that it is created from them or it is the origin of the aliens?

2. How does the goo become a xenomorph if not through pregnancy. In Prometheus Shaw gives birth to a very large face huger which in turn makes her in a way a temporary queen.  it doesnt make sense that the goo needs a fertile host in order to create a xeno, there must be an alternate way and obviously not by contact because of the ginger zombie.

Any decent thoughts on this cause im coming up short.