bisonchat.net is a private Jabber (XMPP) server.
If you want an account on this server contact William.
If you don't know who that is or don't know how to contact him, then chances are this is not the Jabber server for you.
Note that if you join this server, the administrator (William) has a certain amount of visibility into your actions. This is common to any Jabber server or other federated service like Email, Mastodon, etc. Basically, the administrator can potentially see unencrypted messages that you send, unencrypted files that you upload, etc. The administrator can also see your jabber contact list that you sync to the server (not your general phone contact list). The administrator might even be able to see the password that you use for your account! (So don't re-use a password!) There might be some other information the administrator can see. I don't intend to spy on users, but you need to be aware of the situation.
If you want to join a public Jabber server you can find lists like this or this.