That is explained in the link I sent you.
OK, I will ask then as I through the pack to pass to the client player IStamina values?
The SimpleNetworkWrapper field you created has methods for sending packets you want SimpleNetworkWrapper#sendTo(IMessage, EntityPlayer) which will send the data to the specific player.
I know how to send! How send do I stamina to pass the data inside the package?
new StaminaUpdateMessage(stamina);