Topic: Is build-essential package necessary in a debian-apache2 RoR install?

Hi, I am a newbie in RoR.
I am trying to set up my enviroment.
I try to stick in the guide http://wiki.rubyonrails.com/rails/pages/RailsOnDebian
There is mentioned that the build-essential package should be installed.

Could someone explain me the reason? In first sight seems to me
sth technical-pro like stuff needed for programmers building(compiling etc)
packages and not ror newbie-tutorial like stuff.

Thanks . Chomwitt.