You always type commands into the chat window but if it's a valid command, it won't show to other players. If it's showing to other players, the commands might not be configured/you might not have the proper privileges.
Chat with our AI personalities
Use the gamerule 'commandBlockOutput'. The command is - /gamerule commandBlockOutput false . This will remove any annoying chat messages.
On a Minecraft server, chat is always on. If one of your friends can't chat, then it is a problem on their end.
In single player you cannot open the chat box without mods. In multiplayer you press 'T'.
The deafult key to open the chat is T.
Yes. Go to multiplayer settings > Chat= off.