rvroadbirds,
I'm not much ahead of you, but I was asking the same questions very recently, so since I'm still not experienced enough to give you a good written explanation, allow me to provide you with some helpful links.
First go to the Open Forum, right below where you posted this and look for SmokinOkie's Brisket 101. It's very helpful and informative.
This site was also very good.
Brisket Information This information is included in that same site, I'm just saving you looking for it. Clicking on the radio buttons will give you several different views of a packer cut brisket.
Virtual Brisket Finally, this is a link to a post I made recently on the forum, concerning the first thing I fixed in my Smokette, which was a packer cut brisket I got from Sam's and it came out great. Sam's has flats and packers in Cryovac. If you have a Costco near you, I believe they also have comparable briskets.
My First Brisket Hope this helps
Pat