Hi, use this
Code:
on *:JOIN:#Channel_name:{  
  describe # welcomes $nick -- Welcome to $chan ,How may we help you? We hope you enjoy your stay in #
}


Or you can use this.
Code:
on *:JOIN:#:{  
  if $istok(#channel1 #channel2 #channel3 , $chan , 32) {
    describe # welcomes $nick -- Welcome to $chan ,How may we help you? We hope you enjoy your stay in #
  }
}


These codes will work for you, but if you are running it in more than one channel, I recommend the 2nd code.
PS: you can add as many channels as you want, separate them with spaces.

Regards,