Springs:
A spring is just a length of metal wire bent into a coil. A straight wire held vertically will not flex, held horizontally it will flex easily.
Rate is the measurement of a springs strength. A spring with a rate of 100 lbs/inch will compress one inch when you place 100 pounds on it. With 200 lbs it will compress 2 inches and so on. You can use any scale you want. Inch pounds, Kilograms per millimeter, Newton-meters, it’s all the same.
Springs are strong or weak. They are made of metal and therefore do not get harder or softer with a rate change. Correct nomenclature leads to a better understanding of how things work.
Springs hold up the weight of the bike and rider in the correct part of the travel. In the correct part of the suspensions travel!
Pre-load is the energy stored in a spring by mechanically compressing it. A set of .95 kg/mm fork springs that have 20 mm of pre-load on them have 38 kg (83 lbs) of energy stored in them before adding the weight of the bike.
Pre-load does not change the strength of a spring. Just like flexing your muscles does not change how strong you are. It just stores energy (work) in the spring. Notice that it’s harder to control movement when your muscles are flexed than when they are relaxed.