First off how do you connect to BYOND using telnet

You use the IP address of the BYOND world, and the port it is hosted on. To my understanding, most telnet clients have no problem connecting to BYOND. You will sometimes be stopped after connection by a prompt asking you to press enter to continue. Once done, you will be connected.

Also are there any telnet games to connect to on BYOND

Commonly telnet support is implemented into chat 'games'. The Saloon is one notable example.

Also is there any support for any form of authentication

Not natively in BYOND, no. You will have to perform your own authentication in DM once the telnet user is connected, to confirm their identity. Telnet clients will have an IP address as their identifier.

I also meant to ask how many people if any actually use telnet...?

That's kind of a question beyond our capabilities to answer, we don't collect statistics on games especially. However from my own anecdotal experience, it is used by a few people to connect to chat 'games', hence most decent ones will include proper support for telnet.

The general caveat with telnet is it's an unauthenticated, unencrypted protocol. As such it's generally not used across the internet or in networks. It's more common modern use is to act as a protocol over serial link to system-on-chip devices like routers, TV set-top-boxes, industrial equipment etc.