Javascript read help

Hello.
I am barely starting out with JavaScript, and would like to know if it is possible for JavaScript to read input from a certain input box, and respond to it accordingly. I already know how to use if statements.
For example. I currently have an input box, and I would like to have JavaScript "read" what I have in there and respond.
Like.
If I type in the box "hi", and click go. I would like to use the "document.write" command (or any other command) to have it say "go away".

Or anything of the sort. I am using notepad by the way, not sure if it matters.