1) Did you put that code in a Remote file?
2) If not, then put it in a remote file and try again.
3) If so, (or if it still doesn't work), are you trying to get it to say hello in the channel when you type hello? If so, then it won't work, as you can't activate your own on text events (I'm going to partially presume you know this, since you said you did read the help file).
4) If everthing else is correct, check that the person trying to activate the script isn't in the ignore list of the person/bot/client that is running the script.
5) If all else fails, check the status window of the client that has the script, and report back the details of any error messages, or if none, details as to what is/is not happening when the command is used.