Question on Flat Rate Shipping?

[Tim'sTurnings]

I see that most people will ship some of their for sale/sold items with "USPS Flat Rate Boxes". Is this the Priority shipping flat rate boxes from USPS? I just saw snake skins that were sold and will be shipped in a medium flat rate box for $5.95. When I look at the USPS site and at the post office the Priority Medium Flat Rate box has the price at $12.95. I have some turning and pen stuff I want to sell but I don't know how to go about the shipping part. Is there a flat rate box that is cheaper that the priority boxes free from USPS? If so, where do you get them? The easiest and cheapest rates and boxes are for priority boxes that I see at the USPS site but I don't think the prices are jiving with what is listed on any of the classified sections in forums. Is there another way? I am confused and would like to figure it out from you people so I can list my items for sale but I need to know the shipping rates for the listings. Is everyone using the priority flat rate boxes or something else?
Thanks to anyone who can clear this up for me.
Tim.

 

[sbell111]

1) They are using the small flat rate boxes, not the medium ones.
2) Paying for shipping online is cheaper than doing it at the post office.

 

[Tim'sTurnings]

Thank you for clearing that up for me about USPS flat rate priority shipping sbell111. Have a great day.
Tim.