these arrows & line uses for
representing relationship between different entities.
A model is not complete unless the relationships between elements are described properly. The Relationship gives a proper meaning to an UML model.
see this image, you will get difference between all these relations
Generalization describes the inheritance relationship of the object oriented world. It is parent and child relationship.
Generalization is represented by an arrow with hollow arrow head as shown below. One end represents the parent element and the other end child element.
Dependency is an important aspect in UML elements. It describes the dependent elements and the direction of dependency.
Dependency is represented by a dotted arrow as shown below. The arrow head represents the independent element and the other end the dependent element.
Association describes how the elements in an UML diagram are associated. In simple word it describes how many elements are taking part in an interaction.
Association is represented by a dotted line with (without) arrows on both sides. The two ends represent two associated elements as shown below. The multiplicity is also mentioned at the ends (1, * etc) to show how many objects are associated.