Inheritance: It is a relationship with a class and the relationship is IS-A
example: Audi IS-A Car

Association: It is a relationship with a class and the relationship is HAS-A
examples:
Employee HAS-A EmployerIDDetails
Employee HAS-A ContactInformation

Aggregation: It is a type of association. The relationship between the class is HAS-A. Existance of both the class does not depend on each other.
example:
Employee HAS-A ContactInformation

if there is no Employee class still you can use ContactInformation class for other classes like Student, Customer etc

Composition: It is a type of association. The relationship between the class is HAS-A. Existance of one of the class depend on the other.
example:
Employee HAS-A EmployerIDDetails

if there is no Employee class then you cannot use EmployerIDDetails with any thing else