I'm assuming you meant packets, not packages.
Packets are units of data that is sent between an origin and destination.
In this case, the origin and destination are the server and the Tibia client.
In TFS, these packets are called NetworkMessages (msg).
The Tibia client sends these packets to the server.
The server accepts the packets and processes them.
And most times, the server sends the packets back to the client for confirmation.
Let me give you an example.
If I press the right-arrow key, the Tibia client will recognize the action and send information to the server about the action.
In this case, the Tibia client will send a packet identified with a byte, 0x66, to the server.
The server will accept the packet and read the data on it. It will read 0x66 (and sometimes other information).
The server has to do something with the packet (parsePacket(msg)), else nothing will happen in the Tibia client.
In ProtocolGame, this is where all the parsing takes place.
parsePacket(msg) will take the identifying byte and match it with a task.
We pressed the right-arrow key and the client sent us a packet identified with 0x66.
When parsing that packet, we will eventually end up using
this line.
This line will call Game: PlayerMove(), which runs a lot of stuff in the server to process the player's move, like checking to see if the player can move to the new position or not (blocked, like rocks and trees, etc), updating the player's position, etc.
At the end of the server's processing of the player move, it will send a
confirmation back to the client to visually show the movement.
So, basically, the Tibia client sends packets to the server for the server to process and confirm back to the client.
Now, in your question, when he says you have to add 5 packets ProtocolGame.cpp, he's basically saying that the Tibia client has 5 new things that sends packets and the server needs to recognize those packets. If the server doesn't recognize those new packets, then nothing will happen. Like, if the server doesn't recognize 0x66 (which is move east), then the character will not move east at all.
I know this is a long post, but I hope you understood most of it.
If there's something that is incorrect, I apologize in advance, this is the closest I can get with my knowledge on network messages.