One prepare UML diagrams to understand a system in better and simple way.A single diagram is not enough to cover all aspects of the system Sand UML defines different kinds of diagrams to cover most aspects of a system.
One can also create a set of diagrams to meet your requirements. Diagrams are generally made in an incremental and iterative way.
There are two broad caetgories of diagrams
- Structural Diagrams
- Behavioral Diagrams