Just like “ban”, this isn't so special, but let me explain the args (arguments) for you:
?warn [@user] [reason]
?warn @Tazio#4200 Eating Dyuli’s chocolate :( <3
This also saves in the database, but this is much simpler:
Person who did the warning
This will always stay in the database, after 3 warnings the user who typed the command will get another message asking if you want to mute him/her.