A spring system is like a big slinky. When you stretch it out, it wants to bounce back to its original shape. So when you push or pull on the spring, it pushes or pulls back against you. This is called "force".
The force that a spring system creates depends on a few things. One is the size of the spring - the bigger it is, the more force it can create. Another is how much you stretch or compress it - the more you stretch or compress it, the more force it creates. And finally, it depends on what the spring is made of - some materials are better at producing force than others.
Spring systems are used in all kinds of things. They're in mattresses to help you sleep comfortably, in car suspensions to help absorb bumps in the road, and even in pens to make the ink come out smoothly. So next time you play with a slinky or jump on your bed, remember that you're interacting with a spring system!