Step 1: Transfering the template to a useable form
Print it as a half page and then fold it in half. When you print you might want to print the image upside down so that the fold is in the right place and the image on the left of the page!
You can add your own greeting inside and you are all set - oh yes you have to purloin some envelopes from somewhere or other. Maybe take them from less worthy greetings cards that you have left over from last year! The only expense involved here is paper - and print cartridges!