Basics

When creating your mod with the CustomNPCs API you will want to:

    @Mod(modid = YourMod.MODID, version = YourMod.VERSION, 
        dependencies = "after:customnpcs")

or if its required:

    @Mod(modid = YourMod.MODID, version = YourMod.VERSION, 
        dependencies = "required-after:customnpcs")

To make sure CustomNPCs is loaded first.

Simple event handler:

    public class CustomNPCEventHandler {
        @SubscribeEvent
        public void onInteract(NpcEvent.InteractEvent event){
            //your code
        }
    }

To register your event handler:

    NpcAPI.Instance().events().register(new CustomNPCEventHandler());