This is a simulation of interference of waves.

1. Click on "Left Only" and you will see a single wave pattern.
2. Click on "Right Only" and you will see another single wave pattern which has its origin at a different place.
3. Click on "Both" and both waves will be produced simultaneously.

With both waves being generated, observe how the waves interfere constructively in some places and destructively in other places.
You may adjust the separation of the sources by using the slider and observe how the pattern changes.