You're asking about "keyboard broadcasting" and "software boxing".

Take a look at the Guides, then click through to the "software" link in there.

I can pretty much guarantee that Keyclone will get you up and running quickest if you're willing to spend US$20, but there are free options available too, all discussed and compared in the Wiki.

As you're obviously just starting out, the following resources will come in handy at various points on your journey of discovery:

Software tools forum

Forum search facility

Better, but off-site search facility

Wiki

Video - how to set up your first group in WoW