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Class
A class defines the structure and behavior of it's instances.
It holds a collection of the names of instance variables instances have.
printIt - Class instanceVariablesString.
A class holds a MethodDictionary, mapping messages to Edit Methods. These methods are precisely what is updated when you accept code in the browser. This dictionary is also where the Virtual Machine looks for the code to run for a message.
InspectIt - Point methodDict
Classes take care of lots of details - having a name that's global in the system (that's why writing "Point" above worked), keeping track of variables known to all the classes' instances.
Many of the most important things classes know, they inherit from their superclass Behavior.
It is Behavior that holds the method dictionary, and keeps track of the classes' superclass (see Inheritance).
Playing with Behavior is one of the ways that Squeak lets us do radical things like playing with other representations of objects (for example, Objects without classes - aka, prototype systems).
After you're comfortable with classes, you should investigate Metaclasses. In a way, they're sort of "the Dark Side of the class". OTOH, they help classes be objects themselves.