Email and Usenet were the big things for me initially. I used elm for email and tin for news.
As best I can recall, Usenet groups were the way I initially found out about stuff, which at the time was either things you could download via anonymous ftp (back to tartarus, I still had to use XMODEM or whatever to get it to my PC) or topical mailing lists (or LISTSERVs) you could join.
Mailing lists then became a source for finding out about other mailing lists, or new files to download via anonymous ftp.