I need a simple gmail script (on google scripts)

I have two bits of simple code used for forwarding emails on gmail.
I would like to have an automatic google script, which will forward all emails which has certain label (invoices) and after it's done forwarding them, to move them under another label (Forwarded).
As mentioned in title, the code needs to be changed to work on our email.
I have learned how to do programming, but that was 10 years ago and I feel rusty nowadays. I prefer to give the task to someone experienced and up to date.