To join the C2A Discord server you will need to be invited by a member. The invite will be a URL which you can open in a browser or directly into the discord desktop or smartphone app by clicking on the add server icon shown below.
This button appears on the left side of the Discord app and website. Clicking it will open a dialog to either join a server with an invite code (a URL) or to create your own.
To chat with C2A on a Teamspeak server you will need to be invited by a member. The invite will be an IP address and a port nubmer along with a password. You can join temporarily from the Connections menu or by adding a bookmark from the Bookmarks menu so Teamspeak will remember these settings for you.