[Koha] Shelving Location?

We got Koha successfully installed and our data is almost fully migrated and the catalog is fully searchable. However, we are unsure how to define shelving location? I know that the value in stored in 952$c, but when I add an item, there is nothing in the drop down box to choose from. Obviously, I have to add my own, but I don't see where to do that. Help?