How to create a type ?

Hello,

I am trying to understand how works CREATE TYPE, but it seems to
be too difficult for me...

Can someone help me ?

I have tried this :
----------------------------------
create function personne_in(text)
returns personne
as 'select $1;'
language 'sql';

create function personne_out(text)
returns text
as 'select $1;'
language 'sql';

create type personne (
internallength = variable,
input = personne_in,
output = personne_out
);
---------------------------------
but it is full of mistakes.

Even a simple example in language 'sql' will help me.

Thanks,
Ines.