I am going to try to help you make sense of these terms and also explain to you a simple way to test whether a mattress is offering you the support you need for a peaceful nights sleep.
Choosing the correct mattress firmness rating
The only proper way to test a mattress is to lie on it - preferably on both your back and side. To test how well the mattress supports the spine when lying on your back, place your hand in the small of your back.
hover over the images to see the spinal alignment:
If when you lay on your back on the mattress with your hand under the small of your back there it is not enough room for your hand, it's squished and tight to remove, this mattress is too soft for you. Also check your spinal alignment, maybe best you ask someone else who can see you better. (Best take a friend or partner with you!)
If when you lay on your back on the mattress and you put your hand under the small of your back and there's lots of room to move your hand around, this mattress is too firm for you.
If when you do the test on a mattress and it is a snug fit but easy to remove your hand then this mattress is offering you the correct support, you are getting the best benefit from the springs, but don't forget to check from your side also to make sure it is keeping your spine nice and straight.