Mass Effect 2 (PS3) Plot Decisions Question

Ok so last week I got Mass Effect 2 for the PS3, having never played the first one. When I went to my local gaming store, I saw that they had a used copy for $10 less, so I immediately snapped it up, figuring that since all the DLC were already on the disk, there would be no real loss for buying used.

Everything seems to work fine, but I have come across no way to make the important decisions from the first game that influence events in this one. At least, not the major seeming stuff, like whether to save the council, or Wrex, or a couple other decisions that I've read about. I ended up watching the action comic on youtube and it seemed like some important decisions have been made without my input.

How does one make these decisions before playing ME2? Is there a menu that I didn't read fully? How is the action comic supposed to be downloaded? In my case, did someone buy the game, take the important DLC and sell it as used? Am I going to be forever locked into the choices that seem have been made for me?

Should I go back and complain at the store and trade up for a new copy?