You may be confusing Discord with Steem.
It's easy to understand why since every community talks about Discord and their Discord servers but they are actually a different thing.
Discord is a third party software, and a centralized one, where users can create their servers for free and create a community inside those.
Simply go to Discord's official site, sign up and get your server.
Then you just have to create invites and send the link for people to join.
You can't create discord channels on Steemit. Discord channels are created in Discord servers. Discord servers are created by the users of Discord, a multi platform chat application. If you want to create a server on Discord, you need to sign up by visiting https://discordapp.com/
You can't create a Discord channel that runs on the Steem blockchain. That's just impossible right now. It would be very cool if we could have a Discord type of app that runs on the blockchain in the future though!