Postgresql triggers

I have a table containing salesmen, structure follows:

CREATE TABLE agenti
(
  id bigserial NOT NULL,
  agent character(7),
  nume character varying(50),
  nrreg character varying(50),
  cnp character varying(50),
  superior character(7),
  tip character(2),
  gest character(1),
  CONSTRAINT pk PRIMARY KEY (id)
)

I also have a table containing information about the money that will be given to the salesman if he sells an amount of merchandise. The table has the following structure:

CREATE TABLE comisioane
(
  id bigserial NOT NULL,
  agent character(7) NOT NULL,
  nume character varying(100),
  "admin" character(3) NOT NULL,
  nivel smallint DEFAULT 0,
  comis1 numeric(18,2) DEFAULT 0,
  comis2 numeric(18,2) DEFAULT 0,
  dela integer DEFAULT 0,
  panala integer DEFAULT 0,
  CONSTRAINT idx PRIMARY KEY (id)
)

So when an external application inserts a record in the "agenti" table, the trigger must insert a number of records in the "comisioane" table.
Expl:
After the insert on agenti:
insert into agenti (agent,nume,nrreg,cnp,superior,tip,gest) values ('A001103','Some salesmans name','xxxxx','yyyy','A000000','PF','A')

the trigger must do the following actions:

foreach (select admin from administrators) as theAdmin do
begin
      insert into comisioane ('A001103','Some salesmans name',theAdmin,1,0,0,1,49)
      insert into comisioane ('A001103','Some salesmans name',theAdmin,2,0,0,50,99)
      insert into comisioane ('A001103','Some salesmans name',theAdmin,3,0,0,100,149)
      insert into comisioane ('A001103','Some salesmans name',theAdmin,4,0,0,150,199)
      insert into comisioane ('A001103','Some salesmans name',theAdmin,5,0,0,200,249)
      ...
      insert into comisioane ('A001103','Some salesmans name',theAdmin,20,0,0,800,849)
end;


I am new with triggers so I need some help with this.
Thank you