and how do i use it? Sorry if this is an old question.

That is the cheapest way to send books through the mail. When using media mail, only books can be sent( the PO sometimes opens mail to check). This means that you may NOT include anything else (bookmarks, notes, letters, business cards). Not even a note saying "Hope you enjoy the book(s)." The price difference can be great - $2.50 vs. $6 or more.

Media mail is available through the post office, all you have to do is tell the person at the counter that you are sending a book and want to send it media mail.  As Jason said, it is the cheapest way to send almost all books (books under 6 oz are cheaper through first class for some reason).  If you use PBS postage, it will automatically give you the media mail rate.

you CAN include an invoice (like if you use the 1 page printout and put the bottom half in the envelope and use the top half on the outside)

That is usually what I do.  Saves on printer paper and I don't use the PBS wrappers since I have found that they don't hlod up all that well here.  I use the bottom of the1 page PBS sheet inside and use the address on a mailer.  I usually get PBS postage and DC.  I've had PBS automatically give me First Class when it was possible.

Ruth

Actually now books under 7 ounces are cheaper to send by First Class.

Thanks you guys! I appreciate it so much.