How to handle a requirement for nextval

I am still struggling on a few issues, have got my first little database
up and running, and am quite happy with PostGres, but I cannot figure
out how to create a table which can have a field that autoincrements..
I am sure that somewhere in the oid terminology it is built in, but I
want to have a counter on some table entries.. ie...
CREATE TABLE clothing_type (
type_id INT NOT NULL,
description TEXT,
for_sex CHAR
);
INSERT INTO clothing_type (
description,
for_sex
) VALUES (
'pants',
'm'
);

What I want is that the Primary Key (Only Key) be type_id, and int, and
the first item that I insert should have type_id as '1', next will be
'2' etc..
I could have every insert into this table include a type_id, but that
seems unessary.
Can I have something like default='nextval' ?