OpenCV refers to CvArr as
"metatype", "used only as a function parameter". JavaCV implements this by making CvArr the superclass of the types it stands in for, like IplImage and CvSeq. It's not really supposed to be used on its own. What issues are you having exactly?
http://opencv.willowgarage.com/documentation/index.html is a must-have site for OpenCV programming if you're looking for reference material.