creating postgres tables by passing a string to function

I am storing data separated by month.
How do I perform Inserts and Selects based on something like this.

select * from (select  'shipped' || '0509') AS aShippingTable

The table 'shipped' || '0509' exists.

I am scanning barcode labels which have the '0509' on them and I want to 
move the data
to appropiate monthly tables. '0510' would represent shipped on 2005 
october.

Eventually I want to create, insert, select all based on passing a string 
such as '0509'  to a function.

I am a newbie.
Thanks in advance
-Scott