How i will use "Trigger" clause in MS Sql?

INSTEAD OF triggers commonly have to perform at least one SQL command (UPDATE/INSERT/DELETE) as they are executed, instead of the command that fired them. You have to design them carefully keeping in mind upcoming schema changes. Sometimes you simply have to hard code the field list and remember to change it in the future as needed. As an example, if you have to insert a row into a table with an identity column, you can't just insert into <table> select * from <another table>.