are you looking for a tutorial on iptables or on ipchains?
try pointing your browser at the linux Documentation Project
i use this quite often to find information about linux stuff,
or for example if i wanted to block a particular mac address using iptables, i would do a search on Google
for iptables +mac address +block +howto
and it will find pages of tutorials that are specific to what you want, alternativly do a search here at linux questions ( click search on the top right ) chances are that some one has asked this question already
the older tutorials are normaly about ipchains which is being phased out of general use because iptables is more powerful with what you can do with it
hope this helps, slightly