How do you connect several springs to increase the equivalent stiffness? What is one example from industry or other real-life situations where this occurs?

Answer: the answer for that question is the springs should be connected in series.

-we can consider the segments of a helix arrow as springs in series

Explanation:

a characteristic of this system of springs is that, performing a free body analysis for each of the springs follows that, the force applied to each of the springs is the same.

This is the fundamental characteristic of the springs that act in "series"