Type /chatlist to see which channels you're in and their numbers. Then /join name adds one and /leave number drops it. Each channel gets a number, so /1 hello talks in channel 1. The channel names in Forever's starting zones and cities may differ from older versions, so /chatlist is the reliable way to check.

The commands

Command What it does
/chatlist Lists the channels you're in, with their numbers
/join name Joins a channel, or makes a new one
/leave 2 Leaves channel 2
/2 text Talks in channel 2
/s, /y, /p, /g Say, yell, party and guild
/w Name text Whisper. Use the full name the game shows, since names in Forever are unique only as a whole. See playing with friends

These are the standard WoW chat commands. They work the same in every version we know, but we haven't run each one in Forever.

Give a channel its own tab

Right-click a chat tab and pick Create New Window. In the new tab's Settings, tick only the channels you want. Trade and looking-for-group chat in their own tab keeps your main chat readable.

Add-ons for chat

Add-on What it does
Prat Timestamps, class colours, copyable links and history
Chattynator A modern chat frame with tabs, filtering and copyable chat
Block Blizzard Chat Channels Keeps default channels like Trade out of your chat on every character
WoW Translator Explains WoW slang and abbreviations seen in chat

All four had Forever versions when we checked. For more, see chat add-ons.