There are NOT many places to learn the basics of ISIS, the HOW's and WHY's of the protocol. Cisco has a lot of information on ISIS but not really for the beginner. Try www.certificationzone.com.
This site provides an excellent intro and even some advanced details. However, to see the advanced details you must subscribe ($$). Not pushing this site, but it's where I got started. Of corse having several routers will also help.
PS. Different versions of IOS will provide different results so be careful!