Association is a relationship, where one object uses the functionality of other object by sending a message and data to it.
Example:
Association relationship between “company” and “Employee”
Association relationship between “Student” and “Teacher”
Aggregation is a special form of association, which means that an object is the container of other objects.
Example:
Aggregation relationship between “Plant” and “Garden”
Relationship between “Basket” and “Apple”