Resonance occurs when a source of energy oscillates at the natural frequency of a structure. The video demonstrates and explains Barton's pendulum, resonance on a string/wire at the fundamental and harmonics, in longitudinal waves in a spring and in a flat sheet.
In the video I use a simple home made vibration generator, details of which are here:    • Making a vibration generator for free...  
Supporting notes on resonance are here: https://www.fizzics.org/resonance-of-...