What is second normal form and explain it with simple example?

Example: The following relation is in First Normal Form, but not Second Normal Form:

Order #CustomerContact PersonTotal1Acme WidgetsJohn Doe$134.232ABC CorporationFred Flintstone$521.243Acme WidgetsJohn Doe$1042.424Acme WidgetsJohn Doe$928.53

In the table above, the order number serves as the primary key. Notice that the customer and total amount are dependent upon the order number -- this data is specific to each order. However, the contact person is dependent upon the customer. An alternative way to accomplish this would be to create two tables:

CustomerContact PersonAcme WidgetsJohn DoeABC CorporationFred Flintstone

Order #CustomerTotal1Acme Widgets$134.232ABC Corporation$521.243Acme Widgets$1042.424Acme Widgets$928.53

The creation of two separate tables eliminates the dependency problem experienced in the previous case. In the first table, contact person is dependent upon the primary key -- customer name. The second table only includes the information unique to each order. Someone interested in the contact person for each order could obtain this information by performing a JOIN operation.