E-R diagram in DBMS(ER Notation)

There is no standard for representing data objects in ER diagrams. Each modeling methodology uses its own notation.
All notational styles represent entities as rectangular boxes and relationships as lines connecting boxes.
Each style uses a special set of symbols to represent the cardinality of a connection. The notation used in this document is from Martin.
The symbols used for the basic ER constructs are:

Entities are represented by labeled rectangles. The label is the name of the entity. Entity names should be singular nouns.
Relationships are represented by a solid line connecting two entities. The name of the relationship is written above the line. Relationship names should be verbs.
Attributes, when included, are listed inside the entity rectangle. Attributes which are identifiers are underlined. Attribute names should be singular nouns.
Cardinality of many is represented by a line ending in a crow's foot. If the crow's foot is omitted, the cardinality is one.
Existence is represented by placing a circle or a perpendicular bar on the line. Mandatory existence is shown by the bar (looks like a 1) next to the entity for an instance is required. Optional existence is shown by placing a circle next to the entity that is optional.

How to draw E-R Diagram ?

While designing database using E-R diagrams, you should use the following guidelines:

Do not introduce unwanted attributes.
Merge the entities with common attributes or purposes.
Decompose complex entities to simplify them. Do it by decomposing complex attributes into sub-attributes.