Here's an example of what was created when my Fedora 14 system was installed.
[root@athlon network-scripts]# cat ifcfg-eth0
My Fedora 10 system looks like this.
[root@athlonz network-scripts]# cat ifcfg-eth0
# nVidia Corporation MCP51 Ethernet Controller
I don't know anywhere that these variables are explained. However, you can look at /etc/sysconfig/network-scripts/ifup-eth to see how some of those variables are used. And you can look there and ifdown-eth for references to other variables that can be coded in ifcfg-eth.
ps. edit your profile and add what distro or distros that you use. it makes answering questions easier. i'm assuming red hat, centos or fedora for my answer...