I want to make a script where when if a certain person posts in a channel then i automatically type a certain phrase.

For example, whenever user "bob" types something into #channel123 then "jri" (me) automatically types "hello".

Type /help on text in mIRC. There are a variety of examples right there to do what you want. Just change the text to whatever you want.

You can use something like this;


So whenever someone write hello you response like,

Hello, and the nickname of the typer of Hello.
Whenever you respond on nick then you will response Hello whenever Bob types something.