Usenet could (and still can) be operated via telnet using the NNTP protocol [1]. The whole protocol is ASCII-based, just like HTTP, and works via simple text commands. The most common way to access Usenet back in the day was over dialup.
Sure, but the most common way to access Usenet/NNTP servers was through graphical GUI software or "TUI" for those that preferred terminals. Most people didn't write NNTP commands directly, although I did that because I wanted to learn the protocols (same with POP/SMTP/HTTP that are surprisingly easy to get started with)
NNTP worked great with dialup. You could connect and download all the new content since the last time you were online and catch-up offline without blocking the phone line. The clients were designed to work both in both online and offline mode
[1] https://datatracker.ietf.org/doc/html/rfc977