SET IDENTITY_INSERT ON
]) allows explicit values to be inserted into the identity column of a table.
If it is OFF, you can not issue INSERT statements, that affect an identity filed.
If you want an identity filed to work on it's own, just omit that filed from the insert statement.
Let's suppose, you have this schema:
CREATE TABLE [dbo].[students](
[id] [int] IDENTITY(1,1) NOT NULL,
[name] [varchar](50) NOT NULL,
CONSTRAINT [PK_students] PRIMARY KEY ([id] ASC)
Than you can use this DML statement:
insert into students(name) values('John');
...and the server will add the next available value to the [id] field.