Usually you'd find one BBS through word of mouth, and that one would have listings of systems which were hopefully a local number.

There usually had just the one line so users were limited to a certain number of minutes a day before they were no longer permitted to sign on. Sometimes a shareware game or new "Demo" would make to to a BBS and it might take you a week or two to download the entire thing because of time limits.

Some systems gave you extra time if you uploaded new content to encourage sharing. It was kind of a neat system, and I miss how small it was.

I think Telix was just one popular modem program of many.

Just Google for "BBS" i.e. bulletin board system.

They worked over phone lines. Normally you would know about one BBS from a computer magazine and then that BBS would have a megalist of other ones on it.

Telix[0] was just a terminal emulator, to find dial up systems you generally got information offline, such as via magazines or friends, and then got to know other systems from there, or from lists like the FidoNet node list.

[0] https://en.m.wikipedia.org/wiki/Telix

You would come upon a ZIP file and alongside its primary payload there would be one or more ads for various BBSes.

Sometimes the ads were the payload: https://en.wikipedia.org/wiki/ANSI_art#Scene