Why are entity relationship diagrams used?

Entity Relationship (ER) diagrams are drawn when designing a database system, After the systems specification, an ER diagram is drawn showing the conceptual design of the database, this diagram shows the type of information that is to be stored in the system and how these information associate with each other (e.g. one-to-one, one-to-many, etc).

ER Diagrams are simple and easy to understand, thus, this diagram can be shown and explained to user representatives for confirmation and approval.
use of er diagram