Some people have a difficult time transitioning from a layer based editor like Aftereffects to a node based piece of software like Nuke. This video shows you some of the common problems some people experience when trying to learn a new application.
For those of you ambitious enough, the Foundry actually has the whole 1000+ page Nuke manual on their site for free. The file is a PDF and is a must in my opinion if you want to further explore Nuke.
Enjoy, and feel free to comment.