It sounds like you're just describing methods at this point; not specifically class methods.
In the message [cat feeding], the message "feeding" is sent to an instance of an object "cat." That means the "cat" object that received the message would execute its "feeding" method.
One real benefit of Objective-C objects, though, is that they have methods that can seem intuitively similar to the things they represent. [cat meow] and [cat scratch: (other object) pieceOfFurniture] might be more appropriate methods to implement.
A "class" is a basic definition of a kind of object -- something that could be used to create discrete instances of "cat," for example -- and its instances run methods. Classes can have their own methods too, but -- as someone was saying -- their uses are more generic and limited. If you're not sure, there's no need to use them.
I think the two best resources for this are Apple's document "Programming with Objective-C" and, maybe even better, Stanford's introductory iOS App Development course on iTunes U.