You can view a database structure in the standard ERD (Entity Relation Diagram) form. ER diagrams are available for all tables and schemas (databases).

ER diagram for a table shows the table itself and its relations with other tables inside the schema. To view the ER diagram for a table or view, double-click the table or view in the Database Navigator and then, in the Database Object Editor, switch to the ER Diagram tab:

To view the ER diagram for a full database schema, double-click the schema name in the Database Navigator or the previous node in the path (usually - Tables):

NOTE: Table and schema diagrams are read-only. You can rearrange the layout, drag-n-drop elements inside a diagram but you cannot save the changes state or delete/add anything. This is because the diagrams represent the actual state of databases.