Animation shows interference of waves from two point sources. The white circles can be imagined to be crests and the black circles can be imagined to be troughs. The cyan line passes through points where interference is constructive . On this line you can see crest and crest or trough and trough combining. The red line passes through points where interference isdestructive. On this line crest and trough combine.
You can change the wavelength of the waves and the distance between the sources using scrollbars. There are options for viewing thick or thin lines to suit individual taste and an option to turn the pattern off to have an uncluttered view of the ripples. The option of no ripples would allow only the lines of constuctive and destuctive interference to be seen.
Experiment with distances which are multiples of a wavelength and see what happens. Also with the animation stopped, change the distance between the sources and observe cyan and the red curves. Turn off the ripples and change the distance between the sources are the wavelength and observe the pattern of the curves.