People log into the talkers remotely (usually via telnet), and have a basic text interface with which to communicate with each other.
The early talkers were similar to MUDs, with most of the complex game machinery stripped away, leaving just the communication level commands - hence the name "talker".
Most talkers are free and based on open source software.
Many of the online metaphors used on talkers, such as "rooms" and "residency", were established by these early pioneering services and remain in use by modern 3D interfaces such as Second Life.
The first talkers were hosted on an intranet within a school or office or local bulletin board systems that people used to connect to the Internet.