If you pull on a spring like a slinky it’s going to be pretty easy to stretch it, but if the spring is something more like that from a car’s suspension, it will be more difficult– the difficulty in pulling the spring is denoted as K (the particular spring constant).
On the topic of springs you can also understand something about energy.
When the spring is stretched out as far as it can be the potential energy is said to be the highest since it has the greatest pull back to the starting position.
When the spring reaches this starting position on the way back the kinetic energy will be highest since it is moving the fastest.
Once it passes this point though the kinetic energy will start decreasing since the spring will always have the tendency to move back to the resting position.