The first step is to get the HamsterAPI instance to access most of the methods of the API with the static method HamsterAPI.getInstance().

From the HamsterAPI instance you can access the following methods:
getBufferIO() - Util to split/decompress/decode bytebufs into packets.
getBungeeMessenger() - Util to ease CustomPayload communication with BungeeCord.
getReflection() - Optimized util to get NMS and CraftBukkit classes without losing compatibility.
getPacketInjector() - Util to inject/remove HamsterAPI from the pipeline of a player.

You can listen to the following events:
PacketDecodeEvent
PacketReceiveEvent
PacketSendEvent

Decode is ran after splitter & decompress on the pipeline and lets you access to a bytebuf object. You can decode it with BufferIO to get a PacketWrapper object. (Perfect for exploit fixing and security stuff)

Receive/Send is ran after decode on the pipeline and lets you access to a PacketWrapper object. (Perfect for cosmetic/common stuff)

To know how to listen to Events please read the following guide: https://www.spigotmc.org/wiki/using-the-event-api/