A Class is drawn as a solid-outline rectangle with three compartments separated by horizontal lines. The top name compartment holds the Class name and other general properties of the Class (including stereotype); the middle list compartment holds a list of properties; the bottom list compartment holds a list of operations. The property and operation compartments are optional, and you can suppress them.
A Class is a descriptor for a set of objects with similar structures, behaviors, and relationships. The model is concerned with describing the intention of the Class, which are the rules that define it. The run-time execution provides its extension that are its instances.
A Class represents a concept within the system being modeled. It has a data structure, Behavior, and relationships to other elements. The name of a Class has a scope within the package in which it is declared, and the name must be unique, among Class names, within its Package.
Classes are declared in the Class diagrams and are used in most of other diagrams. UML provides a graphical notation for declaring and using these Classes as well as a textual notation for referencing Classes within the descriptions of other model elements.