It's free to join. Sign-up at discord.com. Once you have an account click the purple button above to join our server.
By default all of the rooms on the discord server have notifications turned off. You can override those settings for the rooms that are important to you (eg. The restaurant you want and/or the date you want).
Once you get notified of a dining reservation opening, head over to the Disneyland app or website and book it!