Every time you kill a zombie or "Freaker," you will get a set of ears for each type of Freaker you kill. This much is clear, but what is not clear is that you can turn these Freaker ears in for a juicy bounty. That said, if you want to turn bounties in Days Gone, you will need to find your nearest settlement like the one in Copeland.
You will first visit this location when you find out your bike is stolen early on in the story. However, in every camp or large settlement is a table marked with an ace icon where you can turn ears in for bounties.
Doing so will earn you camp credits that can be used for buying guns, repairing and refueling the bike, and kitchen activities.
You will also earn a small amount of trust that will eventually unlock more items to buy and services you can use. But keep in mind where you turn your ears into, as camp credits are unique to each settlement.
This means camp credits you earn at one camp can not be used for another, and there is also a max limit of 10k credits per camp. But other than that, there is nothing but positives from turning bounties in, so get hunting!