Each post card is quilted on the front, contains a stiff middle "batting", and a piece of card stock on the back so you can write a note. And, yes, they can be sent through the mail. I usually take mine to the post office just to make sure I've got the right postage - usually around $.70. Cards are 4" x 6". Each card comes with a plastic sleeve that can be used as an envelope.
Don't want to send it? Little wooden easels are available for $1.