Discord is a chat service where we can create a community within a Server and base that server around what you want the topic to be like. Like for example, I have a Steemit Server for Discord, and I gather people in this server who loves Steemit.
There are channels I can make within the Steemit Server, for example, I make a channel that is for posting Steemit blogs and there is one for just chatting casually. I have also a channel for rules on how I want each of the channels to work within the server.
Once you join, you will have a clear knowledge on how all this work in action. :)