Illustrate some notations of object modeling notations

A classifier is a mechanism which describes behavioural and structural features. In UML significant classifiers are class, signals, data type, interface, use case, nodes, components, and subsystems.

A class is a description of a set of objects which share same attribute, semantics, operations, and relationships. In UML, it is represented by a rectangle. 

An attribute is a named feature of a class which describes a range of values that instances of property may hold. In UML, they are listed in the compartment just below the name of that class.

An operation is implementation of a service which can be requested from any object of class to affect behaviour. In UML, they are listed in the compartment just below to that of the class attribute.