Responsiveness: It determines how quickly you will feel the response of your Trucks. But also how forgiving your Board will be. Less Responsive equals more forgiving.
Rebound: Springs push back once you release the pressure you apply to your Hangar. The harder the spring, the harder the rebound.
Grip: It determines how much grip your Springs apply to your wheels when pushing down. But also, it is about braking power or in other words how long it takes to slow down or stop completely. Grip also influences how hard or steep you can hold your edge while carving.
Turning: The further you push down on your Hangars the steeper your turning radius gets.