The discord module is used by the bot to send out messages via
the Discord API.
In order to be able to do so, you need a Discord bot token, which
is explained in detail on https://github.com/Nadybot/Nadybot/wiki/Discord

Certain commands also allow sending notification to Discord and the channel
to send these into can also be configured here.

The handling of the receiving of messages is managed by the DISCORD_GATEWAY_MODULE.