Well that information is stored in this file. You shouldn't really change this file unless you have a specific reason for doing so. Everything listed in this file compiles with RFC 1700. The httpd directory contains all the apache configuration files, for the RPM version of apache. Linux does have an AT style service, but the more common system is crontab.
Individual users have their own crontabs that they can edit with the crontab -e command.
This file is discussed in the final lesson regarding kernel compilation. This defines system variables, such as username, paths etc. If you plan on using a modem with your Linux system, you more than likely will want to connect to the Internet. The chap and pap secret files contain password and username information for your ISP if they use CHAP or PAP methods of authentication. This directory may also include some dialup scripts.