This post includes a video showing single slit diffraction of a LASER beam.  The derivation develps formulas to find the diffraction maxima and minima as a function of angle.

Vocabulary:  You need to be able to distinguish between these words, what they mean, and be able to draw diagrams for each.

Reflection
Refraction
Diffraction
(we’ll worry about Interference later)

You need to know:
Huygen’s principle of point radiators.
Similar Triangles
Small angle approximation

Derivation of position of maxima and minima using Huygen’s Principle of Wavelets

Diffraction_Derivation_Part-1: Finding Maxima

 

Difraction Part 2-Full Width of Central Max

Single Slit Diffraction explained.