Help with function

I need some help writing a simple function.

Due to some program limitations for a program I run the db's for, I'm having
to write some simple functions to run some selects. However, I am not sure
how to have them correctly return the record(s) selected and/or how to
properly call them from sql.

Would someone be so kind as to help me with this.

Here is an example function:

CREATE OR REPLACE FUNCTION "public"."test_func" (varchar) RETURNS SETOF
"public"."test_tbl" AS'
Declare
PCN varchar;
test_tbl_rec clmhdr%ROWTYPE;

Begin

PCN := $1;

select into test_tbl_rec * from test_tbl where test_tbl.pcn = PCN;

return test_tbl_rec;

end;
'LANGUAGE 'plpgsql' VOLATILE RETURNS NULL ON NULL INPUT SECURITY INVOKER;

I was trying to call this function from psql using:
select test_func('asdf');

Which returned:

ERROR: Set-valued function called in context that cannot accept a set

WARNING: Error occurred while executing PL/pgSQL function test_func
WARNING: while casting return value to function's return type

What am I doing wrong? I'm in fairly new territory with this type of
functions. I normally have just written simple trigger function that log
table changes.

Thanks for any and all help.

Chris

P.S.

Is there a good website and/or book for learning the intricacies of pgsql?