newbie question about the apt-get install??

[ºØÀí <heligb@163.com>]

I'm often find some maillist descript installing debian package in this way:
apt-get install jade
apt-get install docbook
apt-get install docbook-stylesheets
..
but in debian mirror the full package files isn't similar,such as

apt-get install docbook-stylesheets-------docbook-xsl-stylesheets_1.40-1_all.deb
The apt-get install command can install docbook-xsl-stylesheets package and other useful .deb packages,but how can i know the argument after apt-get install command?
Guess the argument? NO,no,no, My god!