1. Hooke's Law
Stretch a spring, or a piece of metal, and it gets longer. This relationship is explained in this video, along with a method of investigating the behaviour of materials to produce a force-extension graph.
2. Springs in Parallel and Series
If you understand how one spring extends when a load is applied you can then extend this knowledge to investigate combinations of springs in parallel and series. This also has many similarities to the way that combinations of capacitors behave when in a circuit.
3. Elastic Potential Energy
Stretch a spring, or a rubber band, and it stores energy. This is because work is done in extending it. This video explains how to calculate the amount of energy stored.