The extract manufacturers don't usually give information about the grains used to make their extracts. That makes it pretty hard to duplicate their extract on your own.
Fortunately for you, you will have more flexibility in your recipe when you go to PM/AG because you will be able to choose the malts that go into your beer. With extracts, you get whatever the extract maker puts in it.
The types of grain you use will depend on the style you are brewing and your preferences. Each style has it's own characteristics that it gets from the malts. Generally you would choose the malts that give the required character for a style. A good resource to help you get a recipe once you have a style picked out is The Jamil Show:
He has a podcast dedicated to each BJCP style. A couple of good books you could read to help you formulate recipes are Designing Great Beers by Ray Daniels or Brewing Classic Styles by John Palmer and Jamil Zainasheff.
Once you have your malts picked out you'll probably want some sort of recipe calculation program to calculate the specifics of your recipe (OG, SRM, IBU, etc.). A couple of your options are www.recipator.com
(free), Beersmith, Promash, and Beer Tools. I used Recipator for a while and liked it a lot. Other people have used the other programs, and everyone has their own preference. Many of the programs have free trials to so you can try them out.