UML diagrams are like case diagrams, which
gives you a better understanding to summarize
who uses your application or system, and what
they can do with it. Each of it does require you to
follow the proper convention of defining them.
Like for example in Classes Scenario:
The Classes shows a static view of the classes in
a model. The attributes and operations of classes
are along with various different kinds of relationship
that binds the classes together. They can be like
for example, the towns or cities with the relationships
being the routes between those places.