Each diagram represent a different view of your model. The view depends from the diagram purpose. When creating diagrams you should't represent all the details of your model in one diagram. Before modeling your diagram firstly you need to decide what you want the focus of a diagram to be and skip all details that is not within that focus. This help you to make your diagrams readable.
This page provides concepts and purposes of all the diagrams, tables, matrices, relation maps that you can use in the modeling tool.
Each of diagram is described in the following pages: