Before Relay was implemented, one could send a message to someone on another computer if one knew the other person's userid (i.e., screen name or login) and the name of the remote computer system the person was logged into.
To use Relay, one would send a message to a userid called "Relay." This Relay userid was an interface to the Relay program. The message could contain either a command for Relay or a message for a real person at some other computer system.
One could also join a "channel," which was like a chat room, or send private messages.
The time it took for a message to get to a recipient varied. Most of the time messages within the United States didn't take more than a few seconds. Sometimes, however, messages could take many minutes or even hours to arrive.
As a strategy to deal with long lag times, users would talk to many people at once in a round-robin fashion as replies were returned.