Question

How does diffraction relate to the behavior of light as a wave?

Answer 1

I would try using Huygens Principle.

Explanation:

Diffraction refers to the fact that radiation "invades" an area behind an obstacle.
You can see this effect through Huygens Principle, HP, which is quite easy to understand compared to more rigorous tratments (Maxwell Equations, for example) and gives us an idea of propagation in terms of wave-like behaviour.

HP tells us that every point on the front of a WAVE becomes source of secundary spherical waves whose envelope will produce the next front.

When the front meets an obstacle one of these secondary spherical waves can "bend" behind the edge of the obstacle giving us the diffraction effect in the next front:

Try to have a look at this principle, say, on the internet; it is quite interesting!

I hope this can help.