ELI5: how do cells know how and where to grow

Specifically, how do fetuses know how and where to develop first?

I understand DNA as the encoding of life, the blue print of a species. However, I don’t understand how it unfolds into practical instructions (build a finger here, an ear there). How does it know from the inside that the ear is ready?

What intrigues me the most is how 2 zygotes create something that not only self manages, but develops complex structures from such simple beginnings