If light was composed of classical particles...

Here particles all moving in the same direction from very far away hit a barrier with one or two openings.
Collimated particles emerging from one opening Collimated particles emerging from two openings, remaining collimated and not interfering with itself

If light was composed of classical waves...

Here a straight wavefront from very far away hits a barrier with one or two openings.
Wave emerging from one opening, radiating with diffraction Wave emerging from two openings, radiating and interfering with itself

Light is a quantum wave that radiates and interferes with itself like a wave but interacts discretely like a particle

yThis can't really be visualized correctly for a number of reasons, but here is a kind of visual analogy:
Imperfect visual analogy for a quantum wave emerging from two openings
G.Horton-Smith, gahs at k-state.edu, 2010/02/15