create table t(id int identity(seed,increment))

where seed is starting number and increment is number to be
incremented.

create table t(id int identity(1,1),name varchar(50))

so the id will be start with 1 and will be incremented 1 by
1 each time when record is get insered

The identity is similar to squence object in oracle. syntax 
for identity column is
 <column-name> <data type> identity(start value,increment)
ex:
 empno int identity(100,2)

 suppose if u want to add an odd value i.e, 50; u can also 
add 
 first execute IDENTITY_INSERT ON
 and then u can insert whatever values u want. then again 
execute IDENTITY_INSERT OFF

USE AdventureWorks;
GO
DBCC CHECKIDENT ("HumanResources.Employee", RESEED, 300);
GO