how to create a sequence invoice number and insert or update to a column?

Hi, can anyone teach me how to automatic create a invoice number and insert or update it to a column?search in your nearest textbook or search engine for "sql server IDENTITY column"|||C'mon Rudy. You know what is coming next:

"I want my invoice number to have a product code in it, and I want it to look up the last number used for each product code and increment it."