Make sure you open them in a new tab at full view because these puppies are huuuuge! Also make sure you print them out at 100% scale so they fit correctly on the paper. If you print them any smaller, then they will be too small to legally send them in the mail.
And then just cut out, fold, and use a glue stick.
They are free to use. Do not sell these or repost them anywhere.
Send your friends letters, yeah? Nothing beats snail mail.