Need help on triggers - postgres 9.1.2

Hi

I have a postgres 9 database, inside this database I need to create a new table called center_changed that gets inserted by any change that take place in a table called center. So I need to create trigger to do this.

Example:

Table name: center(c_cde, c_dsc, ops_cde, grp_cde);

Now on the table called center , I need to create an INSERT and UPDATE trigger will insert the c_cde  of the inserted or updated center into the center_changed table

Please help me

I have this syntax below, but please help me with the overall query.

CREATE TRIGGER check_center

               BEFORE INSERT OR UPDATE

               ON center FOR EACH ROW

               EXECUTE PROCEDURE check_center_changes();

Thanks