(This is the section that solely explains constructive interference)
The video draws two different waves and displays constructive inference as when the "peaks" of both waves match, and the "valleys" of both waves match as well. By this happening, the two overlapping waves combine to form one large wave.
(This is the section that solely explains destructive interference)
Then, the video displays destructive interference with two overlapping waves with a drawing. However, the way destructive interference overlaps compared to constructive interference is different. Destructive interference, overlaps by the "peaks" matching the "valleys" and vice versa. Because of this, destructive interference actually in the end, forms no wave at all. The two waves cancel out, and later equal 0.
The video explains the doppler effect displaying how the source of the waves moves its original location. In the direction the source is moving, the waves condense, and behind the source, the waves separate. The condensed waves towards the observer have a higher frequency. If the condensed waves are moving away from the observer, they have a lower frequency.
The article defines beats as "the rate at which the volume is heard to be oscillating from high to low volume." The article then explains the common labs of tuning forks and their beats.