Help with connection between crystal and xray

[KFC]

Hi there, I am reading some introduction of crystal and the book mention that we can use the x-ray to explore the structure of the crystal. I more or less understand the idea between that, it is kinda like scatter the incoming wave and observe the outgoing wave. But the mystery stated in the book is that one can infer the crystal structure (like simple cubic or hexagonal) by merely analyze the wave incoming angle (Bragg angle?), why's that? what's the connection?

 

[M Quack]

Read this

http://en.wikipedia.org/wiki/X-ray_crystallography