1. Why do many modern bikes have adjustable suspension?
Standard suspension settings are for the average rider in an average situation. As riders have different requirements the adjusters allow the rider to alter the suspension to suit different situations
2. How do I know if my brake pads are worn out?
New pads will have two grooves machined into the lining, visible from the top when the pads are in the calliper and the plastic cover is removed. The linings are worn out when you can’t see the grooves.