CREATE TABLE employee ( id_num int IDENTITY(100,10), fname varchar (20), minit char(1), lname varchar(30) );

what do the 2 numbers after the IDENTITY clause of id_num column mean?

Here column id_num is defined as the identity column. In the Identity column, the value of the first argument defined the initial value for this column and the value of the second argument defined the value used to add in the last value of this column for getting the next value.