They help eliminate noise. This link should help:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-9.html#post1618425

If you buy Wagner ThermoQuiet Ceramic pads, which I recommend, you don't even need shims. Otherwise, the shims fit over the metal backing plate to the pads. When you remove your current pads, it should be more clear.

No.